AN INVESTIGATION C)? THE QUCCESS CF EARNEGW TROUT i’Qi‘ULfiaflflNfi IN TEN LAKES RELATIVE TO LIMEYENG ENV I RQNMENVFAL FACFGRS Thesis ‘0:- 5510 Deana a? DIM D. MECHEGAN STATE Ffil‘i‘iVERSIW Wayr:e H. Tc-dy 1964': This is to certify that the thesis entitled An investigation of the success of rainbow trout populations in ten lakes relative to limiting environmental factors presented by Wayne H. Tody has been accepted towards fulfillment of the requirements for Ph. D. degree inFisheries and Wildlife flu. @4114 Major proiuegsor Date Fabruary 25. 1964 0-169 LIBRARY Michigan State University OVERDUE FINES: 25¢ per day per iteu RETURNING LIBRARY MATERIALS: Place in book return to move charge from circulation records ABSTRACT AN INVESTIGATION OF THE SUCCESS OF RAINBOW TROUT POPULATIONS IN TEN LAKES RELATIVE TO LIMITING ENVIRONMENTAL FACTORS by Wayne R. Tody The data presented are from a study directed to the determination of the influence of environmental factors on the success of artificially established rainbow trout populations in warmawater lakes. The interaction of growth and mortality is analyzed relative to the efficiency of each population in producing an available stock of trout for the angler. Ten small lakes near the 70 F isotherm in central Michigan were selected as the site for the study. Field investigations were conducted in 1959, 1960 and 1961. Trout were planted in April and May following rotenone treatment the preceding season. Throughout the ice-free season data were collected on trout growth, food habits, and sources of mortality. The lakes were studied simultaneously with regard to physical, chemical, and biological characteristics. In October the remaining trout were removed for estimation of weight and numbers. It was found that the relative biomass of fish present was the dominant environmental factor influencing trout growth. The effect of competition from non-trout fish species was especially effective in delimiting trout growth. It was found that the progeny from a few pairs of adult bluegills caused a nearly complete cessation of trout growth within a few weeks after the hatch of bluegills. Secondarily the relative areas of the littoral zone was of importance in determining growth. The trout inhabited the shallow littoral areas of the lakes throughout the season and fed principally on benthic organisms. All available evidence pointed to predation as the dominant source of natural mortality. Loons and northern pike were associated with heavy losses of trout in two of the lakes. Natural mortality was found to have somewhat more influence than growth on the efficiency of the populations in providing a large standing crop of trout for the angler. On the basis of the experience of this study and a review of the literature it was concluded that rainbow trout can be successfully managed in lakes where competition from non-trout species is controlled if maximum water temperatures do not exceed 78 F in the well-oxygenated zone. In lakes where temperature is relied upon to control competition of other fish species to favor trout maximum temperatures should not exceed 65 F. We'll.l‘“ . Frontispiece. Marl Lake AN INVESTIGATION OF THE SUCCESS OF RAINBOW TROUT POPULATIONS IN TEN LAKES RELATIVE TO LIMIT- ING ENVIRONMENTAL FACTORS by Wayne H. Tody A THESIS Submitted to Michigan State A University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Fisheries and Wildlife 1964 ACKNOWLEDGMENTS I am‘ grateful for the support and facilities provided by the Fish Division, Michigan Department of Conservation, through the offices of Dr. J. W. Leonard, Mr. F. A. Westerman, and Dr. G. P. Cooper in making this study possible. Many employees of the Department furnished assistance whenever it was needed. I am especially grateful to Mr. John Scott, Mr. Roger Wicklund, Mr. O. H. Clark, and the other members of the Lake and Stream Improvement Section for all of the assistance and patience so generously offered throughout the course of this study. I_ appreciate the help of Mr. Paul Earl who drafted the figures. Special acknowledgment is due Dr. Eugene W. Roelofs, chair? man of my doctoral committee, for his valuable guidance throughout the program and for his helpful suggestions on improvement of the manu- script. Dr. Paul Fromm, also of the doctoral committee, was a source of inspiration through his stimulating interest in the study. I amindebted to Robert Carter, Larry Lewis, Alex Strange, and Sandy Sanderson the owners or custodians of the experimental lakes. Not only did they offer the utmost in c00peration and every possible assistance, it became a real pleasure to meet and work with them. TABLE OF CONTENTS . Page ACKNOWLEDGMENTS ...................... ii LIST OF. TABLES ........................ v LIST OF FIGURES . . .‘ ..................... viii INTRODUCTION ...................... , . . 1 Background ........................ 2 THE STUDY AREAS ....................... 5 Mid-Forest. Lodge Lakes, Roscommon County ...... 10 Clare County lakes .................... 11 Mecosta County lakes .................... 12 ESTABLISHMENT OF TROUT POPULATIONS ......... 13 The plants of trout ..................... 14 Test of initial survival ................... 17 FINDINGS ANDANALYSIS ..................... 21 . Trout Populations ....................... 21 Fish sampling . ...................... 21 Fingerling trout ...................... 23 Differential growth of trout ................ 29 Condition factor ...................... 38 Periodicity of growth ................... 43 Survival and mortality ................... 53 Quality of angling . . ................... 59 Dynamics of the trout populations ............. 61 Environmental Conditions ................... 75 Morphometry , ....................... 75 Lake bottom soils ..................... 76 Aquatic plants ....................... 78 Connecting waters ..................... 80 iii Page Chemical and thermal water characteristics ........ 81 Population density and competition ............. 85 Trout activity by water depth ................ 92 Food habits of rainbow trout ................. 95 Predatory animals ...................... 102 DISCUSSION AND FURTHER EXPERIMENTS ............ 104 Environmental factors influencing growth .......... 105 1961 experiments on competition affecting trout growth 111 Mortality . . .y . . ...................... 118 Production...................;......122 Temperature as an environmental factor .......... 124 REFERENCES CITED ........................ 137 APPENDIXES . ' .......................... 141 iv LIST OF TABLES Table Page 1. Size of trout when planted, 1960 ............. 15 . 2. Summary of numbers of rainbow. trout stocked, 1960.. . . 16 3. Numbers of'20 trout surviving 21 days in each of‘two live crates to check initial survival ............ 18 4. Numbersof trout collected and used in growth calcu~ lation,1960...' ...... ,..,._,, ......... 24 5. Mean weight and length of each group of trout at ,end of season, October 1960 .................... 3.3 6. Results of the twonway analysis 'of variance test of growth in weight increments between groups and ' between lakes . ‘ ......... , .............. 34 7. Summary of condition factor (K) for rainbow trout, -- 1960 ............................. 42 8. Growth increments in weight and instantaneous growth rates for consecutive fiveuweek periods in 1960 ...... 46 9. Amount and source of legal trout mortality, 1960 ..... . ' 54 10. Total mortality and corresponding instantaneous mortality rate for consecutive five-week periods in 1960 ................... - ........ 57 11. Mortality and survival of rainbow trout, 1960. Decimal fractions of entire pOpulations .......... 58 12. Monthly summary of fish taken by anglers, 1960 ..... 6.2 13. Summary of plant, production, mortality and mean standing crop for each trout population in 19 60 ...... 70 14. Computation of relative efficiency index. Rainbow trout populations, 1960 .~ .................. 74 15. Accumulative percentage of lake bottom at each depth contour ........................ 77 16. Summary of area, depth, alkalinity and transparency characteristics of the ten experimental lakes in 1960 . . . 86 17. Mean standing crop of trout for consecutive five-week periods in 1960 ....................... 89 Table Page 18. Fishes other than rainbow trout collected in 1960 from the experimental lakes ............... 90 19. Number of trout caught at one-foot intervals of depth in gill nets, 1960 .................. 94 20. Mean depth of trout capture at different seasons, 1960 ............................ 95 21. Percentage of rainbow trout stomachs containing various food items .................... 99 22. Four principal food organisms of rainbow trout in each lake ranked by percent of volume of total stomach contents ..................... 101 23. Rank of each lake according to the parameters of trout success, 1960 ................... 107 24. Summary of trout stocking statistics for experiments on effect of trout population density and young—of- year bluegill competition on trout growth ........ 1 15 25. Comparison of length, weight, and condition factor of trout in experiments on the effects of trout pOp- ulation density and of young-of—year bluegill com- petition on trout growth .................. 116 APPENDIX TABLES 26. Water chemistry profiles of Bass Lake, Clare County, 1960 ....................... 146 27. Water chemistry profiles of Doyle Lake, Roscommon County, 1960 ....................... 148 28. Water chemistry profiles of South Twin Lake, Mecosta County, 1960 ................... 150 29. Water chemistry profiles of North Twin Lake, Mecosta County, 1960 ................... 152 30. Water chemistry profiles of Ryan Lake, Roscommon County, 1960 ....................... 154 31. Water chemistry profiles of Norway Lake, Clare County, 1960 ....................... 156 32. Water chemistry profiles of Little Lake, Roscommon County, 1960 ........ - ............... 158 33. Water chemistry profiles of Slide Lake, Roscommon County, 1960 ....................... 160 vi Table Page 34. Water chemistry profiles of Little Headquarters Lake, Roscommon County, 1960 .............. 162 35. Water chemistry profiles of Marl Lake, Roscommon County, 1960 . . . . . ................... 164 .vii LIST OF FIGURES Figure 1. Frontispiece. Marl Lake ................. 2. Location of lakes in rainbow trout experiment relative to the 70 F isotherm (average July temperature) ..... 3. Contour map of the ten lake basins ............ 4. Rotenone treatment of Bass Lake ............. 5. Method of collecting fish in distress at time of rote- none treatment . ' ...................... 6. Gill—net collection of trout from Bass Lake, July 30, 1960 ............................. 7. Comparison of trout from Bass Lake and Norway Lake, July 1960 ...................... 8. Growth of rainbow trout fingerlings, 1960 ........ 9. Comparison of trout size between Little Headquarters and Ryan lakes, 1960 .................... 10. Seasonal gain in weight of the three distinct sub-groups of rainbow trout, 1960 ................... 11. Growth of legal trout in Little Headquarters Lake, 1960 ............................. 12. Graphic comparison of the final size of the rainbow trout in each of the ten lakes, 1960, based on the mean weight of the combined A and LP groups ...... 13. Synthetic growth curves representing weight of individual trout in each (all groups NC, A, LP combined) of the ten populations, 1960 .......... 14. Absolute growth increments for consecutive five- week periods, 1960 ..................... 15. Relationship of periodic absolute growth of rainbow trout to the instantaneous rate of growth for corresponding periods, 1960 ................ 16. Relationship between temperature and rate of growth of rainbow trout in Slide Lake, 1960 ............ viii Figure Page 17. ' Slide Lake--population dynamics, 1960 ......... 67 18. Diagram of the available trout stock in each of the ten lakes, 1960 ...................... 71 19. Portable'field chemistry laboratory ........... 83 . 20. Method of handling water samples in bulk for field chemical analysis .............. . ...... 83 21. Basin slope, dissolved oxygen content, and thermal stratification of the experimental lakes during period of maximum temperatures in summer, 1960 ............................ 87 22. Field method of stomach analysis ............ 97 23. Comparison of rainbow trout growth in weight in relation to the rate of stocking (pounds per acre) and to competition from young-of-year bluegills ..... 112 24. Comparison of absolute growth of trout in Doyle Lake, 1959, 1960, 1961 .................. 119 APPENDIX FIGURES 25. Temperature and oxygen record for Bass Lake, 1960 ............ . ......... : ...... 147 26. Temperature and oxygen record for Doyle Lake, 1960 ............................ 149 27. Temperature and oxygen record for South Twin Lake, 1960 ........................ 151 28. Temperature and oxygen record for North Twin Lake, 1960 ........................ 153 29. Temperature and oxygen record for Ryan Lake, 1960 .......... . .................. 155 30. Temperature and oxygen record for Norway Lake, 1960 ............................ 157 31. Temperature and oxygen record for Little Lake, 1960 -. , .' .......................... 159 32. Temperature and oxygen record for Slide Lake, 1960 ................ . ........... 161 33. Temperature and oxygen record for Little Head— quarters Lake, ,1960 ................... 163 34. Temperature and oxygen record for Marl Lake, 1960 .................... .. ........ 165 ix INTRODUCTION This is a study of the relative success of rainbow trout stocked in ten lakes offering diverse environmental conditions. In a sense this is a study of production of artificially established rainbow trout pOpula- tions. In a broader sense it is intended as an investigation of environ- mental factors in a lake which influence growth and mortality and thus determine success of the population. The lakes selected for this study range from extremely shallow unstratified bodies of water to deep-basin lakes exhibiting marked thermal stratification. The ten lakes range in size from 3 to 23 acres. In other characteristics the lakes vary widely. Trout were planted in April and May folloWing rotenone treat-- ments to eliminate the existing fish populations. In October the surviving trout were removed, measured in size, and estimated in numbers. Thus the trout were used to test the lake environment for only the ice-free season. Throughout the season, measurement was made of growth rates, and a detailed record was kept of all known mortality. The lakes were studied simultaneously with regard to physical, chemical and biological characteristics of the environment. The dynamics of each pOpulation were computed for the season. It was found that the relative size of the littoral zone and relative pOpula- tion density were dominant environmental factors influencing the rate of growth. Circumstantial evidence pointed to predation as the dominant environmental factor influencing the rate of natural mortality. The interaction of rate of growth and rate of mortality are discussed quanti- tatively as the determinants of production. The efficiency of each pOpulation in utilizing the inherent productivity of the lake and providing a maximum trout stock to the angler are also discussed. Lastly, a review of temperature as a limiting environmental factor is made from the literature and from the experience gained in this study. Background The rainbow trout is a pOpular game fish wherever it is found in nature, or can be successfully distributed from domestic hatchery sources to provide additional angling opportunity. A comprehensive review of stocking as a tool of trout management was made by Cooper (1959). The rainbow trout is often introduced into both lake and stream environments where it cannot be expected to spawn successfully, but where a satisfactory return to the angler will be realized before the stock is completely depleted. It has often been found that lake plantings contribute more to the angler catch both in numbers and weight than do stream plantings. This apparently is true because the lake offers a more favorable environment for both growth and survival than does the stream environment. However, the success of lake plantings varies tremendously. This isespecially apparent when rainbow trout are planted in the warmer lakes, and in lakes with extensive popula- tions of other fish species. It is generally held that trout cannot be expected to succeed in lakes unless at least 10 percent of the lake volume is of a temperature not over 70 F and contains at least 5.0 ppm of dissolved oxygen (Hubbs and Eschmeyer, 1939; Cooper, 1940; Mullan and Tompkins, 1959; many others). Physiological literature on the other hand (Brett, 1956) suggests that rainbow trout can live and grow successfully in waters that do not exceed 78 F for more than a few hours at any time throughout the warm-weather season. In even the shallow lakes north of the 70 F isotherm it would seem that this latter condition could often be met. In such lakes, containing some water less than 78 F with 5.0 ppm of dissolved oxygen at all times during the year, if rainbow trout could not survive and grow at nominal rates (compared to cold-water lakes) it would appear that environmental factors other than temperature must be responsible. It was in this sense that this study was established, to study not only temperature but other environmental factors that might limit trout success in warm-water lakes. Several additional factors exist at present that stimulate interest in the possible success of rainbow trout in relatively warm- water lakes. Many of the small lakes in the north-central states do not furnish satisfactory fishing with their endemic population of centrarchids, bullheads, perch, and other fishes. Apparently these 4 fish utilize the available food supply for reproduction and maintenance requirements with slow growth of the older individual fish. Consequently the fish are small and generally unattractive to the fisherman. The use of toxicants to eradicate these endemic Species is rapidly gaining in popularity as a fish management tool. Many of the lakes where this management practice is desirable (especially privately owned lakes) have generally been considered too warm to support trout. A further interest in the success of trout in relatively warm lakes comes about through the need for an interim species in chemical lake rehabilitation involving stunted panfish control and introduction of predatory game fish species. The purpose of the interim Species is to provide fishing while the other game species reproduce and grow to catchable size. The rainbow trout grows rapidly, is acceptable to the angler at relatively small size and is easily reared in the hatchery; thus it seems ideally suited as an interim species provided that it can thrive in a relatively warm environment. 1Since this study was initiated in 1959 the rainbow trout has been successfully used as an interim species in Michigan lakes follow- ing chemical treatment to control stunted panfish, based on the preliminary results of this study. THE STUDY AREAS Ten small, privately owned lakes representing diverse habitat conditions in the central area of the lower peninsula of Michigan were selected for this study. Lakes of small size were chosen to limit the requirements of hatchery trout and to facilitate field observation. The use of private lakes with restricted fishing enabled some control over population density, and provided creel census data through contract agreement with the landowner. The final lake selection was based on considerations of depth, stratification, and total alkalinity to provide a broad range of individual lake types. The lakes are located near the center of the peninsula where temperatures vary about 25 F diurnally, but average between 68 and 70 F in July, the warmest month of the year in this area (Yearbook of Agriculture, 1941). The location of the ten lakes relative to the climatic isotherms is shown in Figure 2. Six of the ten lakes in this study, namely, Doyle, Ryan, Little, Slide, Marl, and Little Headquarters lie in Roscommon County, on the club property of the Mid-Forest Lodge Association. This club, consisting of 400 members, owns 28 sections of land essentially in a square block. The area is fenced and patrolled against trespass. Two lakes, Bass and Norway, lie to the southwest in Clare County. Bass ‘66" / " ‘\ I, \ aoscouuou I " ‘ x / \\ / 68° I x‘ ,’ II \ 0“ I I so ’ cues I a: ——- _‘ O. / ~\\ / // necosrs ,\ \ 68‘ / \ \ // \\\ \\ 7%. ‘ \\ l / \\ o l I \ 70o- ’ 72~-/ \\.." \\ 70¢ \ I I "" ‘\ _____ "' ----- ‘\ / , ’ \72’ 72" I . Fig. 2. Location of lakes in rainbow trout experiment relative to the 70 F isotherm (average July temperature). 7 Lake is on the Tobacco River Rod and Gun Club property; Norway Lake lies on the Cornwall Ranch. The remaining two lakes are in Mecosta County. These lakes, North Twin and South Twin, are located about 100 yards apart on the Larry Lewis Farm. The investigational work on these private lakes was conducted under a contract agreement. This procedure was well accepted by the landowners. It provided me an experimental facility that was not available (limited fishing) on public lands. A c0py of the contract agreement for 1960 is included in Appendix A. The six Mid-Forest Lodge lakes lie in the extensive sand- plain area of northern lower Michigan (Veatch, 1953). The terrain surrounding the lakes is a glaciated upland of outwash and moraines ranging in elevation from 1, 200 to 1, 300 feet. The local t0pography varies from undulating to hilly. The main soil types are Roselawn and Rubicon (deep infertile sands of high permeability) on the uplands, with poorly drained sands, peat and muck in the limited lowland areas. There is no well defined surface drainage except that Ryan Lake constitutes the source of Benton Creek. Most of the area was originally covered with dense forests of white pine on the wet lowlands grading to red pine on the dry uplands, with scattered groups of hard- woods. At present the area is predominantly covered with aspen, oak and jack pine, with tag alder and white birch on the wet lowlands. Bass and Norway, the Clare County lakes, lie in the morainic region on the southern edge of the Roselawn sand complex. The area 8 surrounding the lakes is hilly with numerous swamps and potholes. The immediate terrain is infertile, gravelly sand, but about one mile to the south, heavier and more fertile soils predominate. Bass Lake has an intermittent drainage connection to other waters of the Tobacco River system through cedar and tag alder swamps. Norway Lake occupies a small pothole in a Roselawn sandy soil area with no surface drainage. The surrounding land is covered with an aSpen-oak forest. In the Mecosta County area, North Twin and South Twin are located in the Montcalm-Coloma association of soil types. The topog- raphy of this area is morainic and till plain. Local types are diverse with many quite fertile farms intermixed with hilly sand areas and numerous swamps. Pothole lakes and swamps are a feature of the landscape throughout the area. A small stream connects these lakes to two other small lakes within a distance of two miles. These drain to the Muskegon River system. Seepage waters here originate from land of much higher fertility than either the Clare County or Mid- Forest 'Lodge lakes. Only a general description will be given here to introduce the character of the individual lakes. A detailed discussion and summary of the salient physical, chemical, and biological features of each lake is provided later. A map of the lake basins showing surface acreage and depth contours is provided in Figure 3. LITTLE 6.5ACRES LITTLE HEADQUARTERS 6.2 ACRES RYAN I4] AC R ES SLIDE I0.0 ACRES ROSCOMMON COUNTY MID-FOREST LODGE LAKES DOYLE 23.0 ACRES MARL ”.0 ACRES MECOSTA COUNTY LAKES DEPTH CONTOUR MAP or LAKE BASINS Depth in Meters LEGEND m Encroachinq shore .M' Intermittent flow / Permanent flow M Spring SOUTH TWIN 30 ACRES Fig. 3 Contour map of the ten lake basins. 10 Mid-Forest Lodge Lakes, Roscommon County Three of the Mid-Forest Lodge Lakes, namely, Little Head- quarters, Marl, and Slide are similar in several features. All are shallow, unstratified, clear or colorless, contain 953 as the dominant aquatic plant, and precipitate marl. A Secchi disc can be seen to the bottom even in the deepest water throughout the season. Little Head- quarters Lake has a number of nearby cottages and is the scene of much human activity. Marl and Slide are remote forest lakes, generally visited only by fishermen. The original fish population (prior to 1959 rotenone treatment for each lake) of Little Headquarters Lake consisted of golden shiners, bullheads, yellow perch and pumpkinseed sunfish. Slide Lake, surpris- ingly, contained no fish prior to the trout introduction. Marl Lake was populated only with small yellow perch. The remaining three Mid~Forest Lodge Lakes, namely, Doyle, Ryan and Little have a light brown water color, are stratified and support fairly abundant growths of aquatic plants. The lake bottoms are soft, pulpy peat throughout the basins. Little Lake is quite soft with a methyl orange alkalinity of 20 ppm. Doyle and Ryan are moderately hard (70 ppm methyl orange alkalinity). Doyle Lake and Little Lake have extensive shoal areas; Ryan Lake has a sharp drop-off from shore to deep water and a relatively small shoal area. The original fish population of Doyle Lake consisted of small bluegills and redbelly dace. Largemouth bass were introduced in the 11 past but none were found in 1959. Ryan Lake contained many species of fish; the dominant species were bullheads, black crappies, yellow perch, pumpkinseed sunfish and northern pike. Little Lake contained only small pumpkinseed sunfish and redbelly dace. A light winterkill occurred on Doyle, Marl and Little lakes in the severe 1958-59 Michigan winter. Clare County lakes Bass Lake is the deepest lake of the ten and could be considered a ntwo--st0ry" or classical trout lake with some oxygen down through the thermocline. The water is colorless and markedly stratified. Originally the lake provided fairly good fishing for bluegills and largemouth bass. About ten species of fish were taken in the 1959 rotenone treatment. Norway Lake is a rather unusual lake because the water is soft and of a perpetual deep green color. The high pH (9. 0-10. 5) and supersaturated dissolved oxygen content throughout the ice-free season result from a continuous algae bloom. Norway Lake, although shallow, is well protected from wind action and markedly stratified. The lake contained only a few bullheads, yellow perch and bluegills in 19 59. According to the owner it has not produced fish of catchable size since the 1800's and has seldom been fished. Bass Lake is the site of three permanent residences. Norway is a remote forestlake. 12 Mecosta County lakes South Twin and North Twin lakes are hard-water lakes. Both are deep, highly stratified, and possess a narrow littoral zone. These lakes have extensive beds of Ceratophyllum out from shore to a depth of 5 to 10 feet. South Twin is clean, but North Twin Lake is heavily polluted with blood from a shoreline slaughterhouse. In prior years North Twin also received the offal of the slaughterhouse and served only as a sewage lagoon. The lake is characterized by frequent heavy plankton blooms and periodic oxygen depletion. Populations of Cladocera and other zooplankton are high most of the time throughout the ice-free season. Apparently oxygen depletion is a frequent occurrence at the time of the fall overturn and in the winter, with consequent fish kills. i Both of these lakes contained numerous species of fish. South Twin Lake, in the opinion of the owner, furnished good fishing for bass and bluegills. In summary, only Little Headquarters, Ryan, Doyle, Bass and South Twin lakes contained catchable game fish, in 1959. Of these, only Bass and South Twin lakes were considered to provide fair to good fishing. ESTABLISHMENT OF TROUT POPULATIONS The field work of this study was conducted in the years 1959, 1960 and 1961. The general procedure followed was the stocking of hatchery rainbow trout in April and May following a chemical decima- tion of existing fish populations by rotenone poisoning. The stocked fish were subjected to the environmental conditions in each lake for one ice-free season. In late October the remaining numbers of fish were estimated when the lakes were again treated with rotenone. During the season, data were collected on trout growth, condition (K), survival, and causes of mortality to compare with data collected on chemical, physical, and biological factors of each lake. The methods used for the collection of these data are presented in the pertinent sections of this report. The first year of field investigation (1959) was of value mainly in developing experimental techniques and in the gathering of survey information. Trout were stocked in all of the lakes in 1959. Apparently the lower waters of the highly stratified, deep lakes had not detoxified from the early Spring rotenone treatment because a high initial mortal- ity of the rainbow trout occurred. No dead trout were found but the low concentrations of rotenone believed to be present probably resulted in a slow, inconspicuous mortality. All ten lakes were repoisoned with rotenone in October of 1959. 13 14 The field work of 1960 provides the bulk of the data for com- parison of success of the trout population in the ten lakes. The next sections of this report are based on the 1960 investigations. Reference is made to the 1959 work only to clarify the 1960 findings. Field investigations in 1961 were restricted to studies of the effects of non-trout competition and differing pOpulation densities of trout on rates of growth. The plants of trout Both legal2 and fingerling rainbow trout were planted in each of the ten experimental lakes in 1960. The legal trout were introduced in three distinguishable groups. One-half of the legal trout in each lake were stocked during the week of April 17 to 23. These fish were not marked by a fin clip and were designated as the no-clip (NC) group. The other one-half of the legal trout were planted during the week of May 22 to 28. These trout were made up of two groups, each com- prising one -fourth of the numbers of the total legal plant. The first group was obtained from the Paris, Michigan, hatchery and marked by removal of the anal fin (designated A group). The second group was from the Wolverine Rearing Ponds and marked by removal of the left pectoral fin (designated LP group). The fingerling (young-of-the-year) trout were planted as a single group in each lake. They were planted during the week of May 22 to 28, in numbers approximately equal to the 2"Legal" trout in this sense refers to trout planted at an initial length of 7 inches or greater. 15 total plant of legal trout. Experience from the 1959 field work indicated that size differences alone were sufficient for identification of fish planted as fingerlings, so they were not marked by fin‘removal. The trout in each of these four plants were carefully selected for uniform Size by the hatchery personnel and placed in holding tanks prior to shipment. I then intensively sampled each group to determine the mean length, weight and condition factor (K). The estimate of variance of each measurement was very low and is omitted here. The results were as follows. Table 1. Size of trout when planted, 1960 Group NC A LP Finger- lings Length(cm) 20.9 21.6 20.4 4.8 Weight(g) 87.0 98.0 84.0 1.14 Condition factor .953 .973 .989 -- These initial measurements formed the base for all growth calcula- tions when the trout were recovered from the lakes in later collections. A summary of the number of trout planted in each‘group in each of the ten lakes is provided in Table 2. A The number of trout planted was intended to. be at the rate of 100 legal and 100 fingerling fish per surface acre of each lake. It was 16 Table 2. Summary of numbers of rainbow trout stocked, 1960 Legal Legal " Legal Finger- Lake NC A ' LP ling April .201 May 24 May 24 May 24 Little 275 137 137 549 Little qurs. 290 125 125 500 Marl 389 175. 175 700 Doyle 1, 190 >575 575 2, 300 Slide 549 255 255 1, 020 North Twin 206 80 80 327 Bass 335 167 167 669 Norway 238 1.10 110 440 South Twin .195 75 75 305 .Ryan 760 360 I 360 1, 440 Total 4, 427 2, 059 2,059 8, 250 1From 0 to 40 NC fish were released in each lake from the mortality-check crates on‘May 15, 1960. These fish are included here. 17 later found that changes in water levels and errors in the scale of the aerial photographs used for mapping proved the original calculations of surface acreage to be inaccurate. Hence, the planting rates (recom- puted) were somewhat variable. Test of initial survival After the 1959 experience of heavy initial mortality, I decided to determine any similar mortality in 1960 by direct observation. The procedure adopted was to place two live crates in each lake to provide for two independent samples. These crates were 2 x 2 x 4 feet in dimension, and built from 1/2"-mesh hardware cloth. In the stratified lakes they were anchored in the greatest depth of water containing 5 ppm of dissolved oxygen. In the Shallow lakes they were suspended at a depth of about 10 feet. At the time of the April plant, 20 trout from the NC group were placed in each of the two live crates. A daily record of mortality was taken for 21 days, following which the survivors were released. This procedure was duplicated in each of the ten lakes. A similar procedure was followed for the May plants except that 10 trout of the A group and 10 of the LP group were placed in each crate. These trout were not released after 21 days, but were left in the crates and used for other observations. Table 3 is a summary of the data obtained from the live crates. It was evident that no initial mortality of consequence was experienced 18 4.30.3 wet/goose op peoexo yo: 3p ESSSOE . .m .3 952m omoa me can? pomp mopmao 03H 5 30an 8.8.: usages: so 523.88 sqaoaasmam .83 eosszoam Hos mm? Ema .022 .mfiowxow mcocowon Hangman om. esp comm.“ Emma 3.3.84 :35?“ mcfipcm: mo flames mm pomp 3.50.5 oSO N . BLOSSOM can p303? H Hammooosm cm on . Hammooosm on om comm. Hammmooosm 3 cm Hammooosm om cm :35. Show egammooosm 2 S eEnamooosm NH m mmzfioz Hammmoosm om om Hammooosm om om mmmm mflammooosm .3th H o Haummooosm 2 cm EBB 5.82 Hammooosm om cm Hommmooosm mm: om 363m Hammooosm om om Hammooosm om cm 3th Hammooosm 2 m3 Hsmmmooosm om cm 2.32 Hammooosm cm on Hammooosm om om .maopm 6334 Hammooosm 3 S Messiah o o 6334. 653 i sass Show 631.“. mass «0 mmooosm «and» mag mo mmooosm Ema H334 IPII 82 .3355 3:9 zooso ow moumao on»: 02:. mo some 5 name H» mutation “no.5 om mo maonESZ .m 32m? 19 in eight of the lakes after the April plant. The Little Lake fish experienced a complete mortality from rotenone toxicity again in 1960. The lake had remained toxic from the treatment in October, 1959. However, the lake did detoxify before the second plant was made in May. In Norway Lake, trout died in the live cr‘ates whenever the pH rose above 10 which happened on bright sunny days. Apparently few of the free-swimming fish died, as determined by later collecting. Initial survival of the second (1960) plant of trout was high in nine of the ten lakes. In Norway Lake some of the trout in live crates died during periods of high pH (10. 5), but it is doubtful if a significant number of the free-living trout died, as subsequent collections indicated no such loss. Some trout died in the live crates in Little Lake but not from rotenone toxicity as did the trout in the April plant. The mortality in May resulted fromlack of oxygen (asphyxiation) when the crates were placed accidentally in deep water with low oxygen content. In North Twin Lake, however, a heavy loss of fish in the lake waSin evidence both in the live crates and in the free pOpulation. This mortality was due to a severe oxygen depletion resulting from an effort to artificially circulate the lake with a stream of compressed air. Surface dissolved oxygen levels declined to a measured 1. 4 ppm. Many of the trout were observed seeking refuge in the CeratOphyllum weed beds along shore where oxygen levels were as high as 7. 0 ppm during the day. The mortality in North Twin Lake from this oxygen depletion was estimated at 100 of the 359 legal trout planted. This was a very 20 rough estimate; a precise count of dead fish was not possible due to the high turbidity of the lake and the rapid removal of carcasses by turtles. In live crates in North Twin Lake, 39 of the 40 rainbow trout died immediately after the dissolved oxygen dropped to approximately 1 ppm. One trout survived oxygen levels of 0. 6 to 1. 6 ppm for 3 days and was still alive when levels of 5 ppm were restored about a week later. Initial mortality can be summarized as consequential on two lakes. In Little Lake the entire 275 trout of the NC group were lost from residual rotenone toxicity. In North Twin an estimated 100 trout were lost from the NC, A, and LP groups combined, from an induced oxygen depletion. Some slight loss of trout may have occurred in the poorly buffered, highly alkaline waters of Norway Lake. The remain- ing lakes exhibited excellent initial survival of the planted trout. FINDINGS AND ANALYSIS Each rainbow. trout population in the ten experimental lakes was subject to a different environment. Some environmental differences were inherent in the lakes, others were created by the manipulation of the density and composition of the fish population. The lake environments were not static but changed. in various ways throughout the season. In net effect, how- ever, ‘the environment of each lake influenced the growth, mortality, and quality of the planted trout and determined the degree of success of each pOpulation. In this section the findings of the 1960 field investigations are analyzed first, relative to the success of the trout populations; and secondly, relative to the determination and description of environmental conditions in each of the lakes. Trout Populations Fish sampling Collections of fish were made at intervals of 5 to 6 weeks in each lake to obtain data on trout length, weight, and condition. The trout taken by anglers and reported in the creel census were not used for growth calcu- lations, as it proved impossible to get accurate measurements from the fishermen. In each of the five routine collections the objective was to obtain 10 fish from each of the groups of trout to allow statistical tests for dif- ferences in rates of growth. Overnight gill-net sets were employed as the general collection method. The standard 6' x 125'. experimental gill net comprised of 25 feet each of five mesh sizes, 3/4", 1", 1-1/4", 1-1/2", and 2", was used throughout these collections. The depth at which each trout was caught was recorded to provide data on depths frequented by the rainbow trout. The nets were set in locations in which experience indicated the best catches could be obtained per unit of effort. However, many sets were made from 21 22 which few trout were'taken. It is believed that the depths at which fish were taken are probably representative of the depths frequented by the rainbows for each lake. A A few trout were collected in Little Headquarters, Marl, and Slide lakes in July 1960 with a 2, SOD-watt, D. C. boom sh0cker, incidental to night observations of the aquatic environment with submerged lights. This operation revealed the presence of, and furnished some growth data on, fingerling trout that were too. small to be taken by the gill nets. At the conclusion of the study in, October, eachvlake was gill—netted intensively fer several days to collect as many specimens as possible for examination. Each lake was then treated with rotenone to remove the re- maining fish. in preparation for new studies thefollowing (season, The hum-- ber of trout killed was estimated by the Petersen mark—and-recapture method. The mark-and-recapture method involves a number of assumptions: 1) mortality occurs at the same rate among marked and unmarked trout, 2) the marked and unmarked fish are equally vulnerable to collection, 3) the mark is not lost, 4) the mark is recognized and reported, and 5) the marked fish are randomly mixed in the pOpulation (Ricker, 1958). To meet theseconditions as nearly as possible, the follow- ing procedure was used. A known number of 7- to 12-inch hatchery trout were marked by removal of the dorsal fin and were released in each lake. Thesetrout were scatter-planted about the lake 24 to 48 hours prior to rotenone treatment. From 50 to 100 marked trout were used in each lake depending upon lake size. As large a Sample 23 as possible of trout surfacing in distress was collected. To these were added all trout found dead for a two-day period after the poisoning. Population estimation was then computed from the pr0portion of dorsal- clipped fish in the entire collection. I believe that this procedure meets all of the assumptions of the method with one exception. The dorsal-clipped fish may have been more vulnerable to collection than the unmarked (NC, A, and LP groups) as it was my observation that they were more easily picked up when surfacing in distress from the rotenone. If the dorsal-clipped fish were more vulnerable to collection,the method would tend toward a low estimate of the population. I believe the magnitude of this possible error is negligible because the subsequent collection of dead fish after the poisoning would tend to correct any bias that might have occurred. A total of 2, 514 of the 8, 240 legal trout planted were captured for use in the growth studies. A summary of these collections is presented in Table 4. Fingerling trout Fingerling trout were stocked in numbers equal to the legal trout in each lake. The one outstanding characteristic of the fingerling plant in all lakes except Little Headquarters was the extremely high rate of mortality. In the nine lakes the fingerling mortality amounted to about 99 percent. It is not known when the mortality occurred but it is probable that initial mortality was high as very few fingerling trout were observed in any lake except Little Headquarters. 24 .poHHHmHQ can? EHonoH ecosowoa Eon“ 32.3.38 #2: H He Sam SHS SSS SH. SH SH mHH. HHS HHN H33. Sm HS SS SS SSH [HS SS SSH SS HS H3396 SH HS mm «H. SS HH 5 H; «S SS 3860 H S S S m H SH S S S .HSHESESS S SH S SH S 3 SH SH SH S aHE. N S S a S S SH SH S S 33. macaw #4 SH SS SS S. SS SH. NS SH SS SH. Hastnsm S SS SH HH. Ha. Ha mm SS SS SH 8850 H S S SH m N S S S S .HBEBSS S SH S SH SH HH SH S SH S aH3. S S S m 3 NH SH SH SH SH 5:3. a. SS HSH SSH SSH Sam SH -- SSH SSH NHH H3353. S SS 3 Ha. SSH HS -- HmH SS HS 55860 H. H.H Ha SH S S 1 SH S HH .HBESHSSS S Ha S. SS HS S I SH SH mm aHE. S SH 5. mm Sm SH -- SN 2.. SH .23. S 2. SH S S SH -- S SH SN .32 95am OZ- 53H. 53A. .3382 mwmmH opHHm HHmH>H oHHHHwH.. onoQ comm .macpm 5.82 58m SHHHHH ommH .COHHmHsono EBahw HHH pom: mam pouooHHoo 95am some 50.: 30.5 .3 maonasz .v 3nt 25 Fig. 4. Rotenone treatment of Bass Lake. Fig. 5. Method of collecting fish in distress at time of rotenone treatment. 26 27 Fig. 6. Gill-net collection. of trout from Bass Lake, July 30, 1960. Fish are arranged on table according to NC, LP, and A groups. Note uniformity of Size of each group. Fig. 7. Comparison of trout from Bass Lake and Norway Lake, July 1960.5 Larger fish of each pair is from Bass Lake. Upper pair, NC group; center pair, A group; lower pair, LP. group. Note the conspicuous difference in size between lakes. Also note lack of regeneration of the clipped anal and left pectoral fins in this figure and Figure 6 above. 28 29 The fingerling trout planted were very small. The mean length when planted was 4. 8 centimeters and the average weight 1. 14 grams. In Little Headquarters Lake the seasonal mortality rate was .736. Forty-two of the 500 planted were recovered in the growth collec- tions. One hundred and ten fingerlings were recovered in the final rotenone poisoning, and an additional 22 were estimated present. There is every indication that these fish would have made a Significant contribu- tion to the 1961 catch if they had been allowed to remain in the lake. Fortunately, enough fingerlings were captured in Little Head- quarters Lake to determine periodicity of growth. Growth in length is shown in Figure 8. Actually the rate of growth was fairly rapid; the mean length equalled the Michigan legal Size (7 inches) in early October. A few fingerlings were recovered in Slide (10 individuals), Little (22), Doyle (3), Bass (12) and North Twin (1) in the final rotenone tI‘e atment. All of these fish were noticeably smaller than those taken in Little Headquarters Lake. A comparison of the final Size based on these limited data is also made in Figure 8. Differential growth of trout The first population parameter of trout success that I will dlscuss is growth as expressed by the total increase in weight of i - . rldlvldual trout for the season. The trout in the final collections varied 1. lttle in Size between the NC, A, and LP groups, but considerably .mode .550 :H 539% 8.30.3 wcHHaomcc So comCmano 033ch was: coxoan .3.me maotmoaomom oHSHA :H 539% mucomonaoa on: Snow .ommH .mmEHLowSHS «no.5. Bonfima .5 530an .w .mHnH MJo§ .SH.SHm cad. CON 00m lHflBM SWVHO NI 37 Little 7 Little He adquarters Doyle Marl [Slide North Twin Bass Norway South Twin [R yan At the leSS discriminating five percent level of confidence the following significantly different sub-groups were found using either Duncan's or Snedecor's (1956) Q tables: I—Little _Little Headquarters FD oyle _Marl [Slide [North Twin [Bass Norway South Twin [Ryan 38 In following discussions of trout success the lakes will be listed in the above order on the basis of growth in weight. The Significantly different sub-groups indicate that no lake can shift over one rank up or down at the five percent level of confidence, and only Little Headquarters and Marl lakes can shift two ranks at the one percent level. No single comparisons of growth rates will be made within the same sub-groups as listed above. Condition factor The condition factor (K) of the trout can be used as a measure of trout success. Condition factor in this instance is computed K = 100 W (weight in grams, length in centimeters): K is Simply a L measure of robustness of the fish. The condition factor is closely related to the rate of growth of the fish as has been found by Brown (1946), Hansen (1951), and Cooper (1953). The greatest value of K in determining trout success in this study is the additional validation it lends to growth rates throughout the season. High values of K (1. 00+), as a direct measure of robustness, can be considered as an indication of the general well-being of the trout. The NC groups of fish planted in April Showed both an increase in weight and a corresponding increase in condition factor by mid-May. This indicates that they took food immediately after planting and adjusted Quickly to the lake environment (Table 7). Throughout the growing season the rate at which trout grew in absolute weight was closely related to condition factor. In Little Lake, 39 Fig. 11. Growth of legal trout in Little Headquarters Lake, 1960. The larger fish were collected from the lake at the end of the -Season in October. The smaller fish are fresh hatchery specimens selected to equal the Size at which the larger fish were planted, in April and May. 40 41 LAKE ., WEIGHT Little 269 grams thtle Headquarters 263 Doyle 247 Marl 239 Slide 230 North Twin 2|l Bass l88 Norway I56 South Twin I46 Ryan IIO 2 4 6 8 IO I2 I4 INCHES 1 l A l 1 L a l 1 l 1 J 4_l l l I I I l 5 IO I5 20 25 3O CENTIMETERS Fig. 12. Graphic comparison of the final size of the rainbow trout in each of the ten lakes, 1960, based on the mean weight of the combined A and LP groups. 42 .mmde 2m 5 939% m4 cam < mo #83 532 can Umocmsflcw M N .Ema mo mES Hm QBOMM OZ mo M H vmw . vvw. mmw. new. wmm. mmm. mam. mmm. Sim wmm. pom. mam. com. 304 gm. .... mmm. EBB £30m m3. m3. m3. m3. 9;. mmm. mmm. m3. 6382 mvmf wmm. mmm. mmoé moo; Em. coo; mam. mmmm o3; woo; cm”. 354 354 SE. mam. mam. 538 5.32 «No.4 254 m8-..” poo; Hmoé pom. cmoé mam. 031m oooé mam. one; mmm. mmm. mum. m3. mmm. 3th mam. «no; owm. m3. mam. mam. m8; mom. :32 mac; mooé mmoé $0.4 5mm. mam. m3; mmm. .mgocm 336m So; mmoé OOH; mmoé m8; 5m. I .i 235 pmnou‘oo om m on . 3 em 3 cm , ow #00 . «com. 33. ~53. who? ~82 $33» 384 was. 230nm Him 959% 96mm mwmhm>< OZ DZ 83 .303 308:?" no.“ 0: nopowm cowfificoo mo mumafism .p 3nt 43 for example, both the increase in weight and condition factor were high throughout the season. In Bass Lake the trout grew most rapidly in June and July. The condition factor increased from . 987 in May to a high of 1. 023 in July. From July until October the condition factor declined to a final value of . 928. This decline in K, without a compensating growth in length, was sufficient to cause production3 in September and October to be a negative value. A similar negative production during some period of the season was also noted in Ryan, North Twin, and Marl lakes according to the empirical growth data. The regression between condition factor and total increase in weight for the entire papulation was computed. The correlation coefficient (r) of this regression was r = . 876'”. Periodicity of growth This study was designed to obtain accurate information on the periodicity of growth in weight throughout the season. Each plant consisted of uniform-size trout in all lakes. These trout were selected for size at the hatchery to reduce variation to a minimum. Four gill- net collections were made at 5- to 6-week intervals throughout the season on each lake. Large samples of trout were analyzed when the trout populations were removed from the lakes with gill nets and rotenone at the end‘of the season. As discussed under differential growth, the three distinct sub- groups of trout (NC, A, LP) grew at Production is defined as the total elaboration of new body sub- stance in a unit of time, irrespective of whether the organism survives to the end of that time (sense of Ivlev, 1945). Also called total produc- tion (Ricker, 1958), Net Production (Clark‘, et a1. , 1946). 44 parallel rates in each lake. The variation between sub-groups in mean size was less than the variation between lakes. Hence, the empirical mean weight of each trout collection is considered quite accurate even when allowing for all possible errors. The mean individual weight of trout for each papulation is shown by synthetic seasonal curves in Figure 13. Trout of the second plant (in May) were smaller than those present in each lake from the April plant. The average weight of the individual trout in the May sample was thus reduced, causing a break in the growth curve. The seasonal growth of the trout varied markedly between the populations in the ten lakes regardless of the final weight attained. In Little, Marl, Little Headquarters, Slide, North Twin and Norway lakes, the periods of rapid increase were in the spring and fall. In Bass Lake the trout grew most rapidly in June and July and actually declined in weight in the fall. In Doyle Lake the trout followed neither of these patterns, as they increased in size evenly throughout the season. In- Ryan and South Twin lakes the growth was very slow throughout the season. These marked differences in the seasonal growth pattern are certainly due to differences in environmental conditions among the lakes. The specific environmental factors responsible for seasonal variation in trout growth will be discussed later. The mean periodic weight increment along with the correspond- ing rate of instantaneous growth for 5-week periods throughout the season are provided in Table 8. These periodic growth values are W EIGHT IN GRAMS \ 99-h8l LITTLE LAKE {2621476 L. HEADQUARTERS LAKE ’ 1 ‘ 1 1 41 l MARL LAKE 12631-2“ DOYLE LAKE \ fill 1 1 1 1 1 l I; 1 1 1 1 L 1 1 1 SLIDE LAKE )2‘6—1"248 NORTH TWIN LAKE ) 57 / 1 1 1 1 1 1 1 1 1 1 BASS LAKE 207 NORWAY LAKE l65 lg L 1 l 1 l 1 l L 1 SOUTH TWIN LAKE .45 RYAN LAKE / 1112 L L 1 1 1 87 L 1 1 1 1 7 APR. MAY JUN. JUL. SEPT. OCT. APR. MAY JUN. JUL. SEPT OCT. 20 I4 I4 20 5 20 20 I4 I4 20 5 20 DATE OF COLLECTION Fig. 13. Synthetic growth curves representing weight of individual trout in each (all groups NC, A, LP combined) of the ten populations, 1960. 46 m .9; N .2. m .2 L. .S w .3 m .3 $388., Ems? mwmpo>< NA. 3.- m- mo. N. 40.. A 2. om om. E 5mm 5 mo. 2 mo. A... mo. m mm. mm 3.. 2.. E5. £50m cm a. . on 8. o S. a mm. am 5. 5 9502.. m2 8.- 2. mo. A. om. mm 2.. mm mm. mm 33. X: 3.. mm 3. N «0.. m- mm. 2. 9.. 3. £5. 5qu x: mm. mm. NH. 3 mo. E S. 2. 3.. B seam 2: 9.. mm om. S 2.- m- 8. mm 2.. S 222 SA 2. 3. S. 3 mm. mm om. mm mm. 3 2.3a Em mm. 3 so. a. mm. am mm. mm 2.. S. spasm 255 9: am. mm mo. 2 om. em 3. mm -- I «:3 B56 w Edam? w. 23mg w Ewes» w. 2385 w 23...? -32: w .80 m .Emm om .33. £83. 5 .92 m . xmd co .. A. 3mm - 5 b3. - mm 2.3. - mm .932 - cm :64 1309 mUoCmnH com.“ 5 mugged «$95-me m>$zommcoo hem my moan.“ 5.26pm msoocmacmymcflpcm 6:3th Ems? 5 mwcosmpofi 5.30.50 .w 3nt 47 essential in establishing the dynamics of each population and in the computation of production to further evaluate trout success. Data on periodic growth of trout, however, is of value in its ownright and will be discussed here. Most fishery biologists accept the assumption of maximum growth of salmonids. in the late Spring and early summer (Hatch and Webster, .1961). Cooper (1953) found that brook trout in three Michigan streams grew most rapidly in May and June, and growth decreased during the remainder of the warm season. A histogram of the periodic growth data in this study is presented in Figure 14. Even with the large variance among lakes it is clear that the general pattern of rapid growth in these lakes is bimodal, i. e. , spring and fall. The greatest increase in absolute weight accrued in September. An inspection of the instantaneous growth rate (Fig. 15) indicates the 'most rapid exponential growth relative to fish size at the beginning of the season in April and May, a decrease until August, and a sharp increase again in September. Bimodal spring and fall rainbow trout growth has also been reported by Johnson‘and Hasler (1954) for dystrophic lakes in Wisconsin. These authors concluded that high temperature adversely affected growth during July and August. It has been concluded by some investigators that seasonal growth of certain fishes is controlled, at least in part, by endocrine secretions. One recent study (Gross, et a1. , 1963) found that growth in green sunfish was influenced by thyroid activity which in turn was 48 5.82 625 .280 .222 .mumtmsoemmm 2:5 .255 Ewmm .538 £00m 933.52 .mmmm .539 3.an 09. :3 80.3 EmnmoumE 5 can some a3 «coca lowcwaam 3313 .ome .mUOCoQ 0695-03.“ 03280950 so.“ mwcoanoE fkoam 330m0< .3 .wrm w FOO m .._.n_mw Om >15... mm uZDd _N ><2 Owddd _ _ _ _ _ _ our 1 O L l 8 w. m 1 H H. ,_ i ccmzv , “I I .. _, _. I O¢ N 1 9 no m I OO 3 I 00 OO. 49 6me .mcowpma mcwccoamossoo so.“ 530%.. m0 3mg msomcmycgmg 05. 0H. 30.5. Boning m0 Ltsobnu. 330QO 0:00“me m0 aEmcoflwHom .2 .wrm I._.>>Om0 mo DOE ma m 50 m .amm on ._2. 8.52. a .62 8...}. . w o _ _ _ _ A _ 000 3 V N e . 9.0 l m 0k CsiOL. m 9 H V I. e . N 0 oo. 1 so... ,7 .. ON 0 w. I: 00 00 N \0 6 3 M 0... ,1 O H ox .0 m m .. one 9 n . no .N 30: 3922.0: m 1 , . w com .. L oeo m. n H m w. 9 l 8.0 3 vd V w 8 com . omd 50 affected by the length of the daily photo period. Anderson (1959) fed bluegills in cages in a southern Michigan lake and in four constant— temperature laboratory cages at 50, 60, 70, 80 F for a 16-month period. He found that, although the fish in the laboratory aquaria grew faster in the winter months than did those in the lake cages, both groups grew most rapidly in May and June. Anderson concluded from this observation that a seasonal factor, most likely a growth hormone, appeared to operate with temperature to control growth. The observations of this study lead me to conclude that rainbow trout growth would proceed at a constant absolute rate throughout the season with a corresponding logarithmic decrease in the instantaneous rate, except for the influence of temperature. There is no evidence of an endocrine mechanism operating to further influence growth. In referring again to the synthetic growth curves in Figure 13, it is apparent that the trout in Doyle Lake grew at a nearly con- stant absolute rate throughout the season. This was not a chance occurrence as a relatively straight-line absolute growth rate was also observed in Doyle Lake in 1959 and 1961 (Fig. 24). In Bass Lake the trout grew most rapidly in June and July, with slow growth in August and September. South. Twin, Ryan, and Little lakes also showed little or no tendency to bimodal spring and fall growth. All of these lakes are thermally stratified with cool temperatures (65 F) readily available to the trout at a depth of not over 4 meters at the 51 time of maximum summer thermal stratification (Appendix Figs. 26 to 35). The trout in these lakes could escape high summer water temperature by descending to lower depths. Trout were taken at greater depths in July and August than in the spring or fall in the gill-net collections (Table 20), but it was found that they still ranged to the lake surface to seek food. It was in the shallow lakes with no cool refuge area avail- able that the bimodal growth pattern was most prominent. In Marl Lake the trout were exposed to warm temperatures by the extreme shallow depth (average depth 1 meter). In North Twin Lake the trout were forced into the 70 F surface waters by severe oxygen depletion at a depth of 2 meters during July and August. These two lakes showed the most well defined biomodal growth pattern. Little Head- quarters and Slide lakes are also very shallow and exhibited the bimodal growth to only a slightly lesser degree. In Figure 16 I plotted the periodic growth increments for Slide Lake against the seasonal temperature with synthetic curves. Slide Lake was selected for this example as it most nearly approached the mean periodic growth curve of the ten lakes. It will be noted that the growth rate in Slide Lake declined very rapidly as temperature rose from 65 to 70 F in June. Apparently the trout were able to acclimate somewhat to the warm water because growth began to increase in July when water temperatures were in the mid-seventies. The rapid increase in growth in September coincided with a drop in water temperature from 70 to 50 F. 52 (SWVHO) lNBWBHONI HiMOHS) A'IMHBM .ommH 6di opfim 5 ”50.5 3083.2 o 539% mo 3.2 98 mpgmsoafioy «59$on QquoSaHom A: .mfim m._02 _ ..a< Lon mwfi'NO l veg ll \ l \ Om SHfliVHEdWBL BOVHBAV :Jo 53 Survival and mortality Survival or its complement, mortality, is the population parameter that, along with growth, determines the success of a trout population. A high rate of mortality can be expected in any fish popula- tion. C00per (1953) stated that the mortality rate of trout in natural populations is about 97 percent the first year, and 75 percent in succeeding years. In lakes where artificial populations of trout are established, such as in this study, no natural reproduction or recruit- ment of stock can be expected because the trout do not have suitable habitat to spawn. Pepulations thus experience a continuous depletion, the rate of which influences production by offsetting gains in weight and determines the total stock available to the angler. Of. the 8, 545 legal trout planted in the ten experimental lakes, the cause of mortality was determined for 5, 439 or 63. 6 percent of the total (Table 9). The remaining 3, 106 or 36. 4 percent of the trout disappeared without trace and are termed. ”unknown" or natural mortality. These figures are not exact but are close approximations. Fishermen reported taking 1, 457 trout or 17. 1 percent of the total p0pulations in the ten lakes. This figure may be slightly low although all anglers agreed to secure a fishing permit from the care- taker or lake owner and file it with a record of fish taken immediately after completion of the trip. I have no evidence to indicate that this was not done. .mggawomh cam #38 mo mammo— GO @9383me 54 a wdm ado wd Hg; m6 w.m «1mm ode H33 «0 mmmEoonmm nu mg .m I. mmw 6 mm» rmv .H 23 umm mam .m men .m .8283: 2309 me Sm mm mam mmm mom 0 S Em owe; 59mm NH mv mm mom 3 o 0 ma mg“ mg 538 £30m mm mm” we own pm 0 o om 2m mow K9.25.82 3 mm om cow om How 0 om mmm mmm mmmm mm >2 mm mmm ow o H: 3 3. mam 538 5.32 mm new mp “van :. mwm o we. raw mmo .H oEHm me Hmm mm wow S cm 0 o3 3H amp :32 mm mom .3 3 mm; 3 m3. 0 2. NS 3% .m 3.3a 3. mm 3 S... 2 mam o 2 EN 0% .235 323 m 5 Ha mom .vw m mum oH me 3% 3th «coo hon Eco son ~6on mum: 3% mcofi woodman 1.8% -852 28m .552 1550.953 .833 5 $3 noofloo . «no.5 SEA hfifimfioe Eaton“ ococmuom wcfiwcmw 35m: howsoimom :uBOQU no 5: 0333825 2835383 348336 .3 8.26m a 2 H308 owmfi .mpfimfiog «50.5 ammoH mo condom cam ESOE< .m 3nt 55 In the gill-net (growth study) collections, 2, 513 trout or 29. 4 percent of the total were processed. An additional 327 trout (3. 8%) were estimated lost in the gill nets due to mutilation by turtles and crayfish; often only little scraps of fish tissue, or the head of the trout was left in the net. More often the head or tail section was eaten away so that no growth measurement could’be made. The NC group lost from rotenone toxicity in Little Lake con- tributed 275 trout to the known mortality. At North Twin Lake there was a mortality of trout due to oxygen depletion when I attempted arti- ficial circulation of the lake with compressed air. Eleven dead trout were found at the outlet screen, and an additional 100 ($50%) was the estimated loss throughout the lake. . The method of population estimation in the final rotenone kill in October has been discussed previously under trout collection methods. The. estimate of the unrecovered number of trout in all lakes was 756 or 8. 8 percent of the total initial population. This unrecovered segment of the population was low because many trout were removed by intensive gill netting on each lake during the week just prior to the rotenone treatment. All trout taken in the October gill netting and those recovered in the rotenone treatment were included in the 29. 4 ' percent of the population removed for growth collections. Together these sources account for the 63. 6 percent total known mortality. The greatest chance for error in these estimates lies in trout taken but not reported in the creel census, and errors in the population estimates of 56 the final rotenone treatment. These errors are believed to be low in magnitude. The 3, 106 trout not accounted for (36.4%) in the known mortality are designated natural mortality after the method of Ricker (1958). These trout account for 12 percent of the total population in South Twin Lake, the lowest natural mortality; up to 58 percent in Doyle Lake where the greatest natural mortality occurred. The probable causes of this natural mortality will be discussed later. Natural mortality can be considered singly as a measure of trout success. The rate varies between lakes, which reflects the influence of responsible environmental factors. In Table 11 the total mortality of trout in each lake is divided on the basis of Ricker's equation a = u + v; where a = the annual rate of mortality, u is the fraction removed by fishing, and v the fraction lost by natural mortality. In Table 11 the fishing mortality (u) includes all trout mortality result- ing from gill-net fishing as well as the catch by anglers. North Twin Lake is included but the true proportion of natural mortality is not accurately known. 4 In Table 11 natural mortality as a fraction of the total trout p0pulation is provided in column v. Natural mortality as a portion of the entire population, however, is not valid for a comparison between lakes because it is influenced by fishing mortality, which is not constant 4 For practical purposes North Twin Lake is so badly polluted that annual losses from summerkill and winterkill would reduce it to the lowest rank for the year. 57 mow swam . bmo .H ¢N . NNH mm . mm: mm . mmm mm . mom mm . wmfi oww .H Cahm Pm: mmv . ma; m2 . Hm vo . 02 mm . mm NH . am no . w mwm G239 Swzom om: mwm . wmm mm . om. mm . no mo . om mm . mm 2; . mm wm¢ thHOZ 0mm mmm. owm Hm. on NH . om ON. mm PH . moH >0. mm mom mmmm moH Mar . Hmm ON . mm hm . ow HH . ON Pm . owl“ pH . Nm mam £239 £9202 GoaV mmm . mmm m: . mm mm . omH PH . 022 mm. . Nam HH . mm moo .H mvflm mm; cow. Ham 2m . «um raw. ONH mm. om N¢. NHN mm. mHH mmr T82 mmm Nww . Hum .H mm . NQH om . Hmm mm . mam mm . hum ow . wwm owm .N mTAOQ mm NNw . vww om . wm mm . “Va mm . mm mm . Na; mm . Hm own .thUm 0:34 mmH mom . mm.“ ma . mm mm . wv mo . ma Hm . Nm u: it mbm @334 w .«oO Amy poo. poo. poo, hon non mg 365 mt 19.2 HI -852 m. -552 .HI :552 HI -852 m: :832 UmEEQ u>w>s3m :3an -Hwtoa m .200 m show on 33. mm mash. am .32 «no.5 8.312 35832 Hmcommmm 2308 A. .Emm -8 has, .3 «use -mm .82 .8 23¢ penasz @3st a cum: 5 mpowpoa 52095-95.“ m>fisommsoo so“ Al: 3mg 323.38 mdoocmacmsmg wcwpsoammhsoo can 350.5 20 muonascv 5.23.85 2302. .3 3nt 58 Table 11. Mortality and survival of rainbow trout, 1960. Decimal fractions of entire populations. Total Fishing Natural Sur- ,Natur’i‘l mom?” _. ity of fish surViv- mortal- mortal- mortal- viv- . . . Lake . . . ing after fishing ity ity ity al v (a) (u) (v) (s) --- v+s South Twin . 43 . 31 . 12 . 57 . 17 Bass .57 .47 . 10 .43 .19 Little . 50 . 33 . l7 . 50 . 25 Slide .62 .39 .23 .38 .38 Norway . 59 . 32 . 27 . 41 . 40 Little qurs. .82 . 67 . 15 . 18 . 45 Ryan .69 .26 .43 .31 .58 North Twin .711 .16 .551 .29 -651 Marl . 80 . 36 . 44 . 20 . 69 Doyle . 84 . 27 . 57 . 16 . 78 1Includes 100 trout estimated mortality from oxygen depletion N=a+s=1.00 a=u+v,s=1-a v ratio of natural mortality to population OI" v + s :- N - u ' excluding fish removed by fishing. 59 between lakes. A better comparison of natural mortality between lakes is the ratio of loss from natural deaths to the population excluding trout removed by fishing. 1 To explain this ratio, the total trout p0pulation (N) can be equated in terms of mortality and survival as: N=a+s or N=u+v+s In this equation as fishing mortality (11) becomes greater, less fish are available to die from natural causes. Therefore if N is equated to one, as fishing mortality (11) approaches one, natural mortality (v) approaches zero, .and survival (5) approaches zero. Thus the fraction of natural mortality based on the whole p0pulation is not valid for comparison between lakes unless fishing mortality is constant. The best comparison between lakes is to consider the fraction of natural mortality of the pOpulation remaining after fishing mortality has been excluded v 4_ 3 Quality of angling The selection of experimental lakes on private lands where treSpass was controlled allowed an adequate and economical creel cen- sus. Each fisherman was required to obtain a creel census card from the landowner before going-fishing. At the completion of each fishing trip the angler recorded 1) the length in inches of each fish caught and retained or released; 2) the approximate depth at which fish were taken; and 3) a record of the number of hours fished. Each card was then returned to the landowner. 60 The creel census cards were collected on every visit to the lakes by the investigator. This provided an Opportunity for discussion of fishing conditions, and checking on any irregularities in the creel census procedure of which the landowner had personal knowledge. Measuring boards were provided at each lake marked in tenths of inches. This apparently confused many of the fishermen who persisted in recording the fish lengths in eighths of inches. The reported fish lengths were not used in growth calculations. A total of 1, 457 of the 8, 545 trout planted were reported in the creel census. No fishing by anglers was permitted on Norway, South Twin, .and North Twin lakes at the request of the landowners. Fishing'was permitted on the remaining seven lakes, except that Little Headquarters Lake was closed to fishing on August 30 to insure a sufficiently large pOpulation for growth collections during the remainder of the season. Little Lake was fished very little because it was a remote lake, reached only after traveling a long, rough road. As can be expected in a census of this kind not all anglers filled the reports out correctly. The major effort made in checking cards was to insure that all fish caught were reported at least in number. To calculate a catch-per-hour statistic, all incomplete cards were disregarded. On the complete cards 1, 289 fish were reported taken in l, 366 hours of fishing, or a catch per hour of .94 trout. This figure may be somewhat high as some unsuccessful anglers may not have turned in a report. However, any such error is considered negligible. This catch 61 per hour is'high in comparison with similar trout lakes in the area because on these private lake's fiShing pressure was comparatively very light. Fishing success was essentially the same all season, with the exception of Slide, Doyle, and Little Headquarters lakes where the catch per hour declined in August (Table 12). It was observed that a few expert fishermen influenced the catch per hour. These fishermen could take limit catches of 5 trout almost at will. The Doyle and Little Headquarters report of limit catches in Table 12 reflect the presence of these fishermen at the Mid-Forest Lodge. Most of the anglers fished with bait; few of the anglers used artificial flies. Fish were taken principally from depths of 5 feet to 10 feet in May on all lakes, but as the season progressed fishermen reported increasing depth of capture in the deep lakes (Bass, Ryan, and Doyle). Generally the fishermen were very pleased with the quality of fishing- No complaints of poor taste or poor appearance of the trout were reported. Dynamics of the trout populations Growth and mortality have each been discussed as parameters of trout success. The ten lakes have been evaluated on the criteria of (rapid growth, and again on low natural mortality with respect to the trout populations. The concepts of exponential growth and mortality - Table 12. Monthly summary of fish taken by anglers, 19601 62 Month Little Little qu rs . Marl Doyle Slide Bas 3 Ryan Number of fish April -- -- -- -- -- -- -- May -- 97 2 124 77 1 45 June 2 21 58 61 85 34 126 July 3 34 -- 240 60 10 43 August -- 71 -- 43 26 27 16 September —- -- -- -- -- 26 22 October -- -- -- -- -- 103 -- Total 5 223 60 468 248 201 252 Catch per hour April -- -- -- -- -- -- -- May -- .90 .50 .78 1.53 .25 1.10 June 33 .78 1.11 .71 1.41 1.41 1.09 July 20 92 -- 1.31 1. 14 .83 .84 August -- 49 -- . 36 .48 1.08 1.00 September -- -- -- -- -- . 94 l. 22 October -- -- -- -- -- 1.23 -- Average .27 .77 .81 79 . 1.02 .96 1.05 Number of limit catches April -— -- -- -- -- -— -- May -- 9 0 15 12 0 5 June 0 1 9 8 13 5 16 July 0 2 -- 40 7 1 4 August -- 7 -- l 3 1 3 September - - - - - - - - - - 2 3 October -- -- -- -- -- 12 -- Total 0 19 9 64 35 21 31 Percent of total catch 0.0 42.6 75.0 68.4 70.6 52.2 61.5 Nnrwav anth Twin Nnrfh Twin had nn anolina nrpnnnrp 63 deve10ped by Clarke, et a1. (1946) provide a basis for study of the interaction of these factors. On a Space and time continuum, quantita- tive computation can be made of standing crop, production, mortality and survival. In the ten trout populations of this study all of the fish were stocked. A There was no natural reproduction or migration of wild trout into the lakes. Computation of the pOpulation dynamics requires, therefore, only the following vital statistics: 1) number and weight of trout (at the start of the season (actual plants), 2) the rate of growth in weight during successive short periods of the season, and 3) the rate of mortality during the same periods (Ricker and Foerster, 1948). g The number and weight of the trout stocked are accurately known (see page 15, and Table 2, page 16). Only the legal trout are considered in these computations because the p0pulation of fingerling trout present in any lake, except Little Headquarters, was negligible throughout the season. To compute growth and mortality rates the season was divided into five successive periods; each period was 5 weeks long. One-half of the legal trout were planted on April 20 and the other half 5 weeks later in May. The 5-week periods simplified the computa~ tions and eliminated introduction of error as the second period began with the second plant. Periodic growth collections of trout were made at 5- to 6-week intervals which coincided with the termination of each computation period. The final 5-week period terminated on October 8. 64 The standing crop and number of trout estimated present on October 9 was designated as the surviving pOpulation at the end of the season. The trout removed in the final gill-net and rotenone harvest Operation are thus considered in these computations only indirectly as part of the final standing crop. The mean weight of the individual trout (W0) at the start and end.(W1) of each successive 5-week period was extrapolated directly from the synthetic growth curves. The instantaneous rate of growth (g) was computed from the equation: W Vii = eg. and g = loge (WI/W0) (cf. Ricker, 1958 for details of this and succeeding calculations. The actual computation was done by use of Ricker's Tables.) In a similar manner the instantaneous rate of mortality (i) can be computed from the number of trout present at the start (1%) and end (N1), of each period from the following equation: N1 41 _._=e No where a = fraction of fish that die during period. or, _i_= -loge (1- a) However, the date of death was unknown for 38 percent of the trout of the ten populations. It is assumed that the rate of this unknown mortality was exponential. Therefore, the number of trout present at the beginning and end of each 5-week interval was approximated by the following procedure for each lake. The entire season (April 20 through the rotenone kill in late October in this instance) was further subdivided 65 into successive weekly intervals. The known mortality (average 62%) was posted by date into the weekly period of occurrence. The instan- taneous rate of mortality for the entire season was then computed for the remaining fish. The number of fish expected to die (natural mortality) in the first week was then computed and subtracted from the total population. This procedure was repeated for each successive week of the season in conjunction with the known mortality until at the end of the final week the population was equal to zero. I then computed the instantaneous rate of mortality for the total population by 5-week periods corresponding to the same periods for the instantaneous rate of growth. As the fraction of fishing mortality (angler catch and growth collections combined) was known the instantaneous rate of fishing mortality (2) and the instantaneous rate of natural mortality (3) were also computed from the following relationship: 2 + 9. The data is now at hand to compute the mean standing crop (W) for each interval. Mean standing crop is computed from the relationship: ‘ x77; W(8§-«i-f 1) g-i When W equals the standing crop at the beginning of the interval, W is computed simply by multiplying the number of fish present at the start of the interval by their mean weight: ‘All computations up to this point were made on the basis of fish weight in grams. I transformed W- 66 from grams of fish per lake to a unit of pounds/acre by: W (454) (lake size,(A)) The mean standing crop can be multiplied by any instantaneous rate to determine the mass (total weight) of fish involved for the period. These computations were made for each population: gVV = production, total growth in weight of fish for the interval including the growth made by fish that died during the interval iW . total mortality 3W fishing mortality SW = natural mortality, or mortality from all other causes than fishing The population dynamics of Slide Lake are shown graphically in Figure 17. In this graph the mean weight of individual trout, popula- tion size (number of fish), and mean standing crop are plotted for weekly intervals throughout the season. Production and mortality are shown for corresponding 5-week intervals. Five hundred and fifty legal trout Were Planted on April 20. During the ensuing 5 weeks production exceeded total mortality and the standing crop rose steadily. This was true because the growth rate was rapid, and both fishing and natural mortality Were low. On May 20 the second plant of 510 legal trout was made. The inlpact of this plant was to nearly double the number of trout in the popula- tion and also the standing crop. As the mean size of the trout in the 67 8880— cmnEmEom _ .032 63:89? cofiwfisaoaunoxmd opfim .S .5 mu 4.0m ms. C. 4~ommww and o .m mo 38: .833 ..... . o.oo« ma «.3 E on; 2 «.mm «a 98 S o.oo« «.«w OH 92: 92: «2% «.2 m «.8 «.mw o.«« «.«N. m 92: «.3 «.2. 6.3 «do a oé: oé: 0.2: «.3 at: «.8 98 «.8 m «.3 «.3 «.2 «.3 «.8 «a... wnmmufidmw m ode 981% «am “rmwmnanshmmnuwwmw «.3 «.3. u «.3 «.3 a «.8 «.g «.3 9E 93 6.5 «.3 «.m« 6.2. o.«« m «.3 «.3 «.3 «.mm m.o« mam rwwomc m.«« «.2. m.«« « «.3 6.3 «.5 m.«« :w e.o« 9.3 92 «.8 0.2 H 222 .9363 «6me @334 ~33qu swam EBB 539 3th mmmm Annouofiv 3:3 .5qu 566m :53 psoucoo Shop some am Eofion exam mo owmafivonwaofiumgfisncolw .mH oSmE 78 Bass Lake.I--Entire bottom pulpy peat and muck. In profundal zone black, pulpy peat with strong odor of hydrogen sulphide. Norway Lake. --Bottom.near shore a brown fibrous peat; in deeper water it grades into a black, pulpy peat. Entire bottom .is littered with undecomposedleaves and sticks. South Twin and North Twin lakes. ~~Entire bottom is a black, pulpy peat or muck. Aquatic plants Samples of the dominant aquatic plants were collected when the lakes were mapped. Plankton samples were taken only in Norway and North Twin lakes where algae blooms were evident. The more con- spicuous aquatic plants are summarized here, briefly, for each lake. Marl Lake. --Aquatic plants are very scarce. There are a few scattered plants of Najas and Potamogeton and one large Chara bed. Little Headquarters Lake. --Extens_ive Chara beds throughout the lake. Najas is fairly abundant and there are some scattered plants of Nughar, Scirpus, Potamogeton natans, and "I;J amplifolius. Slide Lake. --Extensive Chara beds. Very few‘higher aquatic plants. In late summer many Chara beds rise from the bottom and turn yellow, causing an unsightly appearance to the lake. Little Lake. --Nuphar, Nymphaea, and Brasenia are found in a zone 50 feet wide around the entire lake margin. Submerged aquatics are fairly abundant in the littoral zone consisting of 1:. amplifolius and Utricularia. 79 Ryan Lake. --A dense bed of Nuphar and Numphaea surrounds the lake along the shoreline. Dense growths of Ranunculus and Potamogeton occur down to depths of 10 feet all around the basin. Doyle Lake. --This lake has the most abundant growth of higher aquatic plants of any of the ten lakes. Nuphar grows over about two thirds of the lake area. In the shallow areas dense beds of (3353 and N223 are found. In depths of from 5 to 15 feet many Potamogetons especially _P. zosteriformis occur, succeeded in still deeper water by beds of Nitella. Bass Lake. --A narrow band of Nuphar and Nymphaea around shore. Some beds of Potamogeton border the water lilies. Chara beds border the Potamogetons and extend down to depths of 7 to 10 feet. No plants were found at greater depths. Norway I:a_.k_e_. --No higher plants or Characeae were found. The deep- green water color which lasts throughout the season is believed due to a colloidal clay, and a continuous bloom of blue- green algae of which Microcystis and Anabaena were most common. South Twin Lake. --A rim of Pontederia, Nuphar, and Nymphaea extends out about 25 feet from shore around the precipitous basin. This is flanked by CeratOphyllum beds down to 10 feet in depth. A few other Potamogeton, Myriophyllum, Elodea, and Utricularia specimens were intermixed. No plants were found below 10 feet in depth. North Twin Lake. --A rim of Nuphar and Nymphaea extends around the lake. This is flanked by CeratOphyllum and 1:. pectinatus beds which extend to a depth of about 5 feet. No other submerged aquatic plants were found, but scums of algae and Lemna were common. Frequent algae blooms occur in this lake; Coelosphaerium and Anabaena were common. ad 1 Connecting waters Marl, Little Headquarters, Slide, Little and Norway lakes are completely landlocked lakes. None of them have outlets, but Little Headquarters Lake is fed by a flowing spring. Little Lake has a small intermittent inlet containing a small beaver pond. Doyle Lake is also a landlocked lake. Its outlet seeps away, several hundred yards below the lake, into the porous sandy soil of the area. Doyle Lake does have a small inlet, and the lake level is maintained at present by an old beaver dam. The remaining four lakes are connected to other Surface waters in their drainage systems by permanent inlets and outlets. The outlet of Ryan Lake constitutes the source of Denton Creek. Bass Lake drains through a cedar‘ swamp area to the Tobacco River, and North and South Twin lakes are on a small tributary stream of the Muskegon River. Barrier dams were installed on these lakes to prevent the entry of non-trout species after the rotenone treatment. Inclined screen structures were used at North Twin and South Twin lakes, and outlet screens on the culverts below Ryan and Bass lakes. These devices were not entirely effective as non-trout species were reestablished in all four lakes. Minnows (redbelly dace) were also found in Doyle Lake after the rotenone treatment. No non-trout species were found in Marl, Little, Little Headquarters and Norway lakes after chemical treatment. Slide Lake had no existing fish populationin 1959 when it was selected for this experiment. 81 Chemical and thermal water characteristics To standardize the collection of water analysis data, one permanent station was established at the deepest point in each lake. This station was marked with a buoy which afforded an anchorage point for the survey boat. Water samples were collected with a modified Kemmerer sampler at one-meter intervals from the surface to the bottom to establish temperature and chemical water profiles. As the lakes were small (3 to 23 acres) it was assumed that one profile (located at buoy) would give a reliable measurement for the entire lake. Temperature and Secchi disc readings were recorded directly at the sampling station. Water samples for dissolved oxygen and alkalinity determination were taken ashore and processed in a portable field laboratory (Fig. 19). Water temperature 3 were taken with a Whitney electric resistance thermometer. Some doubts were held as to the accuracy of this device; consequently, it was checked periodically with a standard mercury thermometer and calibrated in the laboratory. An occasional water sample was checked in the field against a reliable pocket thermometer. The temperature data are considered accurate to within t1 F. A complete description of the water temperatures by depths throughout the season is furnished in figures in Appendix B for each lake. Temperature stratification is indicated by connecting lines of 82 Fig. 19. Portable field chemistry laboratory. Fig. 20. Method of handling water samples in bulk for field chemical analysis. Kit is for fixing oxygen samples. 84 like temperature at 5-. degree intervals on a seasonal time scale. In addition, temperature profiles for one measurement in the spring shortly after ice-out, and one measurement in the summer at the time of maximum stratification are furnished in Appendix B for each lake. Dissolved oxygen was determined by the Alsterberg (Azide) Modification of the Winkler Method. Occasional samples were checked for iron interference with potassium fluoride reagent. No erroneous results were detected. A complete record of oxygen stratification is included in the Appendix to correspond with the temperature records. In Table 15, the lower limit of dissolved oxygen is indicated by depth. Phenolphthalein and methyl orange alkalinities and free carbon dioxide were determined by the methods outlined in Standard Methods far Examination of Water and Sewage (1960). A Beckman pocket pH meter and at times a Hellige colorimeter were used to determine the hydrogen ion concentration. Some difficulty was met in the determina- tion of free carbon dioxide in the stagnant waters of the deeper lakes probably due to the interference of organic acids. Profiles are given in Appendix B for phenolphthalein and methyl orange alkalinity, free carbon dioxide, and hydrogen ion content both in early April and mid-August. Water transparency read- ings were taken with a standard Secchi disc on the shaded side of the survey boat. Total alkalinity as the mean of the successive values determined throughout the season are summarized for surface and 85 bottom waters in Table 16. Phenothalein alkalinity is summarized separately as the maximum value determined at a depth of one meter throughout the season. The range in transparency and the mean value are also summarized in Table 16. In three of the lakes--Marl, Little Headquarters and Slide, the bottom was visible even at maximum depths throughout the season. The basin slope of each lake based on the accumulative per- centage of area by depth is shown graphically in Figure 21. The mid- summer dissolved oxygen stratification is shaded in each of the figures at intervals of 5. 0 ppm and 0. 0 ppm. The surface temperature, thermo- cline, and bottom temperatures are also provided. This diagram shows the depth and extent of the profundal areas in the deeper lakes in contrast with the shallow, unstratified lakes. Bass Lake has dissolved oxygen (less than 3. 0 ppm) below the thermocline. In North Twin, the lake polluted with organic wastes, dissolved oxygen declines to 0. 0 midway through the thermocline. In all the other stratified lakes the 0. 0 ppm dissolved oxygen level coincides very closely with the lower limit of the thermocline. Neither Bass Lake or North Twin Lake underwent a complete overturn in the spring of 1960. POpulation density and competition The fish populations of all ten lakes were eradicated in October, 1959 with rotenone, but four of the lakes were re -populated to some extent with non-trout species before the trout were planted the 86 « H76 o 8 2. m .m H. .m «.3 swam « SA « mH« mmH « .H. m .m o .m 55. £56m m .« «-« m m« H: m .m « .m. . H. .HV «63.82 «H «Tm « 3H 8H «.m o .H.H « .m mmmm Ht oH-« m« «Hm 3H H .Ht « .m m .m 539 £82 5: Eaton «H «w «w m .H o .m o .2 82m to: Saxon « 3 «H. o .H o .m a .HH H82 «H mHéH H. H: E H .« o .m o.«« 2.8a H.HHV..EoHHoa «H as 8 . m .H H .m « .m .235 655 a SA 0 «m o« H .« H .m m. .8 2:5 A59: than: Hammv 6.85:5 Hmpopoav :68 5 £83 H.888 Hv 888m 833m swamp chop Amohomv omeon omcmm inficnwfim Homwsoxrw HmHHOmmomv own 855 mos 83A hosoammmswah. 5L3 33:“..me < Edging omcmpoéhfiofi 1308 ISBN -382 coma a: momma Hmucoawpoaxo :3 65 .Ho moSmHHoHomHmno hocopmamfiwnu paw aficfiwfim .5336 6on .Ho mamfifism . ma 3nt 87 0 80° __ III 2 _ . MARL LAKE 7|° 4 .— 0 7 79. _ I 2 I— 4 ’_ SLIDE LAKE _ 68° 6 0 79° _ m 2 _ 68° . }r 4 _ 7' ..“"‘r' .;~‘- 46. m - NORWAY LAKE 7 $2373“? . a: 42 in 6 - '— . Lu 2 o g . 2 .— I I- I— 4 — O... I- UJ H o 6 __ 8 .— 0 79° . n: 2 I— 4: 70° 6 - T a - DOYLE LAKE 60° _ 49° no - '2 P E] 5+ ppm 02 r o-Sppm 02 I4 _ .099!“ 02 LITTLE HEADQUARTERS LAKE 79° 7|° LITTLE LAKE ,_ 69° 79° T 54° ‘5I° RYAN LAKE 78° 7I° . ' 5I° 48° 75° . - 5;... 70° 50° 44° 79° BASS LAKE }T Maximum Thermal Gradient °F THERMAL GRADIENT Fig. 21. Basin slope, dissolved oxygen content, and thermal stratification of the experimental lakes during period of maximum temperatures in summer, 1960. Horizontal axis represents lake surface area on a percentage basis. 88 following April. These four lakes were Ryan, Bass, North Twin and South Twin. A few redbelly dace were found in Doyle Lake. In Little Headquarters, Marl, Little, Slide, and Norway lakes the 1960 fish populations consisted only of trout. Estimates of the mean standing crop of trout in each lake are available from the computation of pOpulation dynamics. These data (for legal trout) are summarized for the season by successive 5-week periods in Table 17. The plant of fingerlings on May 24, 1960, con- sisted of approximately 0. 25 pounds per acre in each lake. Only in Little Headquarters Lake did the fingerling population build up a sufficiently large biomass to be quantitatively measured during the season. In Little Headquarters Lake the final standing crOp of fingerling trout was estimated at 5.0 pounds per acre on October 20. The mean standing crOp for the entire season can be estimated as approximately 2. 6 pounds per acre. The non-trout fish species found in the October 20, 1960, rotenone treatment of Bass, Ryan, North Twin and South Twin lakes are listed in Table 18. The species are arranged in approximate descending order according to their relative abundance by weight. The mark-and-release method of estimation used for the trout pOpulations could not be applied to the non-trout species. It was impossible during the rotenone kill to pick up numbers of the non-trout species proportional to the recovery of trout, as they did not surface and die at the same rate as trout. Some fish, like bluegill and crappie 89 mo .2 EH .m 3. .m we .«H S .2 «a .«H E .m «a .2 8am as .H« Ha .o« m« .H« mo.«« 3. .H« 3.8 mm .2 «H..«« 5.5 58m Hm .mH 2 .2 3 .2 mm .5 H: .o« S .o« Ho .HH H.« .o« $3.82 o« .«« H.« .2 w« .«« S .«« e« .m« «a .«« «Ht .2 «o «H $3 3.2 mm .2 om .«H 2 .HH «H .5 mm .o« ow .«H 5.2 :5. 5.82 mH .o« mm .H« «a .o« S .o« 3 .«« «« .H.« Hm .«H «H. .o« 85 3 .HH HVH .H. Hm .m 3. s Ha .HH 3 .«H 3 .m H.« .«H H32 3.2 a; «ma 8.: 2.3 m«.«H $5 3.2 2.8a S.«H mm .m 2; HH .HH Hm .HH H.« .mH 2.. .m S «H .235 2:5 HH..HH 8.: 3.: Ho .2 «« .«H 35 I 38 2:5 £882 a .69 . . 122.. 686 8.8 w 80 m 36m om .HHsH. .H« 82. H« .32 ha «Momma «568$ - H. 3mm - Hm ““me mmemmwmsmmmewHfi .32 - 8 H244 mwmmwwv 8H3 , HmcHnH co Ema? on? 5 mugged 4395-03“ ofiusoomcoo .HoM Hopom Hod mpcsomv 30.5 .8 mono @3985 $02 .Sogmfi Table 18. 90 Fishes other than rainbow trout collected in 1960 from the ex~ perimental lakes. 1 2 List is in order of relative abundance by weight. Ryan North Twin South Twin Bass Lake Lake Lake Lake Bullheads3 Largemouth bass Bullheads Bluegill Golden shiner Common shiner Bluegill Redbelly dace Yellow perch Bullheads Largemouth bass Creek chub Northern pike White sucker Pumpkinseed Stickleback Pumpkinseed Golden shiner Creek chub Pumpkinseed Redbelly dace Mudminnow Bluegill Pumpkinseed Creek chub Yellow perch Black crappie Shiner (Unident.) Yellow perch Golden shiner Northern pike (1) Redbelly dace Mudminnow Largemouth bass Green sunfish Yellow perch Common shiner Johnny darter 1A few redbelly dace were collected in Doyle Lake. 2Complete list of full common name and scientific name of fishes is provided in Appendix. 3Brown, black, and yellow bullheads are combined; all three species were found but the relative abundance or specific occurrence was not recorded for each lake. 91- fingerlings, appeared quickly after the treatment, while other species such as bullheads did not appear for several hours. A large, composite sample of the non-trout species was collected during the period of distress from rotenone poisoning. All fish in this sample were separated by species. counted, and weighed to determine their relative abundance. No accurate estimate of the biomass of non-trout species could be made. I concluded, simply, that the biomass of non-trout species was considerably greater in all four of these lakes than the biomass of the trout present, and that the biomass of non-trout species (pounds per acre) was :the largest in Ryan Lake, followed by North Twin, South Twin and Bass. lakes in descending order of magnitude. The proportion of adult fish to young-of-year fish varied in each of these lakes. In all four lakes adult fish had the best opportunity to migrate into the lake before the April plant of trout was made. In April the barrier screens were improved and I believe they were quite effective for the remainder of the season. If some adult fish survived the rotenone treatment they would have been present before April as well. Therefore, the proportion of adult fish in each lake pOpulation provides an indication of the biomass of each non-trout population during the season. Many adult yellow perch, northern pike, and bullheads were found in Ryan Lake. North Twin Lake contained a smaller proportion of adult fish in the population than Ryan but moreathan either South 92 Twin or Bass lakes. The dominant species of adult fish in North Twin Lake were the white sucker, common shiner, golden shiner and bull- heads (black, brown, and yellow), South Twin Lake had numerous adult yellow bullheads but very few adults of the other species. Bass Lake contained only a few adults of each species. From this informa~ tion, I conclude that Ryan and North Twin lakes contained a larger biomass of non-trout species throughout the season than did South Twin and Bass lakes. In Bass Lake in particular, the total bulk of non-trout species was apparently very minor until the occurrence of a large bluegill hatch in June, after which time the total bulk increased very rapidly. In South Twin a considerable fraction of the non-trout population was young-of-the-year yellow perch. As this species spawns earlier than the bluegill, it can be assumed that the non-trout population in South Twin Lake built up somewhat earlier in the season. than in Bass Lake. In summary, the total biomass of the non-trout species was the greatest in Ryan Lake throughout the April to October 1960 season, followed by. North Twin, South Twin and Bass lakes in successive order of magnitude . Trout activity by water depth The rainbow trout were found in the littoral areas of all ten lakes throughout the season; Trout were observed jumping or feeding at the surface on nearly all occasions ‘when the lakes were visited-~- even in the months of .July and August. Inhabitation of the littoral zone 93 was evident from the locatiOns at which rainbow trout were taken in gill nets throughout the season. In all growth collections the depth at each end of the gill net was measured before pulling the net and removing the trout. Each gill net had a 6-foot depth of webbing. The location of each trout caught was marked on a simple diagram of the net-set to determine depth of capture. The recorded depths of trout capture for each lake are summarized in Table 19. All trout were caught in depths of 13 feet or less. Efforts were made to catch trout with gill nets in the deep water of Ryan, Bass, Doyle, and South Twin lakes, but the deep sets were never successful. No trout were taken in the gill nets in May from South Twin Lake, apparently the nets were set at depths below the trout pOpulation at the time. The littoral zone of South Twin Lake is only a narrow zone around the lake due to the sharp dropvoff about 25 feet from shore. When the gill nets were set in the shallow littoral zone in later collections, trout were taken readily. Overnight gill-net sets were successful while daytime sets took very few fish. However, it was noted on several occasions that the trout had been freshly gilled when the nets were checked in the early morning hours. It is probable that the trout are crepuscular, i. e. _. most active in the twilight and dawn periods. Based on these observations it appears that the trout were well acclimated to the upper waters of each lake. However, there is some indication that the trout p0pulations did shift into slightly deeper water . 94 mm 8 HS 2. 3H on mm SH SH SH H309 -- -- -- .2 .: -- .3 -- -- -- om -..- -- -- i E. .. i -- -- -- mH ..- i -- i -- -- -- -- -- .. H: -- .. -- .1 .. .. .. .: -- -- S -- -- -- 1 .. .. -- -- .. .. S -- -- -- E. i -- -- 1. -- -- mH -- -- -- -- 1 -- .: -- -- -- «H -- .: -- .. .. H .. i H H. 2. -- -- -- -- -- o .. .. m a «a .. .. -- .: m m -- i H 3 HH -- .. .. H. m a. i -- a H: S -- m -- m m S -- m m on a .. m m H. mm H: m o HH 3 m -- m. m H; mm 3 m m w m a mm 2. 2 o. 3 HH H 2.. S E s mm H: H: m 2 HH o 3. mm 2 m a H: H. m «H H. H N H: m H. m 2 m 3 2 a. m NH 2 o m m 2 m w H m m H; H; m a S H. «H m o S 8 NH Hm H. H .9253 has» 539. 539 . . H32 oHtE 82m mefiv 982 Sim 5.82 fisom 3.89 3am $83 8:3 Sumo 82 .3ch Es 5:33 Ho 2.28:: 88H “m. Ewsmo 39:. so 3852 .mH £nt 95 in the deep, cool lakes with the advancing summer season, and then moved back into shallower water agaijnin the fall (Table 20). Table 20. Mean depth (feet) of trout capture at different.seasons, 1960 Season Lake Bass Doyle Ryan May 4. 6 2.0 4. 2 June 8.0 3.1 3.2 July 9. 7 6. 4 7. 9 September 5. 0 5. 9 7 . 7 Food habits of rainbow trout The availability of food organisms as an environmental factor influencing trout success was measured only indirectly in an analysis of trout food habits. Limitations of time precluded direct measurement of the invertebrate populations of each lake. At each of four periodic trout collections (approximate dates: June 14, July 30, September 5, October 20) an analysis was made of trout stomachlcontents. This analysis was restricted to the legal trout, ' but no differentiation was made between the NC, A, and LP groups. . Fish of varying sizes were selected and Opened until ten stomachs containing food materials were found. Some of the collections, however, did not contain ten stomachs with food contents, and in these cases the 96 analysis was conducted with the sample available. To avoid the necessity of stomach preservation and rehandling, the analysis was completed directly in the field. The contents of each stomach were spread in a shallow container. Each organism, or food material, was successively identified and the following information was recorded: 1) the number of stomachs containing each different organism, 2) the estimated percent, by volume, that the organism comprised of the total contents of all stomachs, and 3) an estimate of the total number of individuals of each organism for all: stomachs. A summary of the percent of stomachs containing various groups of food items is presented in Table 21. From this summary it can be concluded that bottom organisms were most frequently taken by the rainbow trout; organisms from the surface film were the next most frequent group; free-swimming organisms and aquatic plants were eaten less frequently, but were of considerable importance in certain lakes. A large variety of food organisms was taken by the trout, but relatively few groups made up the bulk of the diet. Dragonfly nymphs stand out in importance. They constituted a major item of the diet in seven of the ten lakes. Diptera larvae, Hemiptera (Notonectidae , and Corixidae), and small molluscs were important food items in most of the lakes. Chaoborus were important where they occurred in abundance (two lakes). The higher aquatic plant, CeratoLhyllum con-~~ stituted half the volume of the stomach contents in South Twin Lake. 97 Fig. 22. Field method of stomach analysis. 98 99 -- -- o.oH 98 H. .2 -- E -- m .H.. m .HH 885.5 .H.... .0. .HH m .H. as v.2 cs. o.oH m .HH H..mH -- 8888. m. .mm m .3 -- m .3. H .H. as o.oH .. m .m .. 8&5 323a ofimsv< Rom -- m.m -- -- m.~ -- mam -- ms .< 8885 9mm -- -- -- -- o.oH as H; 2 as 3.. 88933888? of ms ms -- H..oH cs Ham 3.. Hum H.H. .H.. 8.89 o .2 m. .NH m .H« m .HH H .H as. o .2 m .m m .HH o .8 .H.. orangésmaofloo o .2. m .H. o .8 H. .mm H. .H« o .3 o .8 m .3 m .3 a .H.... «885% mEmEmwpo sodium -- -- m .m -- -- m. .H.. -- H .H. -- -- 8.883 I. H .HH .. o3 H..oH -- .. -- -- -- 38E 9m w .HHH. m .S -- -- -- m .H.. -- -- ad... 888820 - 8.885 m .m can 94..., m .m m .3 -- .. -- -- m .3. 8882.5 .. a .HH H. .HH -- m .H.H H. .HH I a .HH m .m H .H. 828$ 28080th . mfimwsmwgwafifikm . 8 ohm m .m m .m n- m .m -- u- u- -- i .. EmHRmuOV sombmoomdmz m .3 Him o.oH 93 -- can 98 P.H.H 93. m .HH , 88382 as -- m .H. Ham H..HN -- m .m H .H. .. .. 3850 m. .N can 92 m .8 a .3 m .H« H. .2 -- m .m H. .5. 38838888988885 0.2 m .m o.mH -- -- as. I. -- as H .H. 3:880:35 -- H .HH -- -- H. .2 c .mm m .3 m .3 o .8 -- 9: 8.882882% -- H .m -- -- Hamm m .H.H 98 His” 98 N .3 9: 88803.2. m .H.” m .8 m .H. H28 -- m .Ha 98 m .8 9H: m .mm @288me Mango . . mfimgwao Eotbm 8H; any 83 82 83 SH; 82 $2 82 3.2 . £3. £5. - 88% macaw pooh swam fisom 83.82 mmmm 5.82 meHHm mica H82 235 2:3 . . 8H3 J .oxfl some Eon.“ mEofi poo.“ its msomEoum .«o .8955 93365 memosusmnwa 3 «3.33% .mfimfi boom 9526..» 9:53:00 mnomfiowm «no.5 3085.2 .3 ommuswouom AN 3nt 100 A summary of the four principal food items of the rainbow trout in each lake is presented in Table 22'. These findings agree with those of Hatch and Webster (1961) for rainbow-trout food habits in the Adirondacks. Burdick and Cooper (1956) found. also that rainbow trout in Weber Lake, Wisconsin, fed principally on bottom organisms. Leonard, et a1. , (1948) reported that bottom organisms comprised 40 percent of the diet (of small (7" to 12") rainbows, but that 30 percent of the total diet was fish. I found that troutin three lakes ate fish but only the trout in Bass Lake ate fish (small minnows and centrarchids).in appreciable quantity. Small fish were eaten in Bass Lake during the late summer season when the K factor was decreasing and the trout were actually declining in weight. Johnson and Hasler (1954) state that rainbow trout feed almost exclusively on 200plankton from May through October in Wisconsin dystrophic lakes. No similar pattern existed in the lakes of this study, although Cladocera Were important in the trout diet in three lakes. Some trends in the seasonal change of diet were observed, but the number of stomachs analyzed was not‘large enough to draw rigid conclusions. In general, Chironomidae,.Chaoborus, and other Diptera larvae, occur in the stomachs in June and July. Dragonfly nymphs were taken all season but were less frequent in September and October. Corixidae, Notonectidae, small molluscs, fish, and aquatic plants were taken most frequently in the fall. 101 .mEmFHcH 3.8st 98 Ema 2333:2033 paw ancU mccsHoE omjw m .cmscm cam: :oEEoo cc: H: 6cm: cam moans: oflficcwom .mEaE cHBmEHHHH .3 .ASwQHoEHQ ccHEcmctHQcH chB .ccExEoU cam ccpfiocsouoz Ecoxc .muoccg 03¢:on :43 NH m 8:88 8&5 mm 888885 mm H5889: .989 H...“ €58.85 Sim H H 858820 HH 8882.20 H.H .5885 mm 3.83 8&5 5.5. 58m H. H m momszoz oH noccd m m mUSoccowoZ 3 msponomso .ANBHOZ H H H. EEocoHEo Ha biomass mm m 8382 mm is mmmm w H. 825.80 S .2sz mm 888820 3. 8885 .892 5.5. 5.82 H N 88::on m 2.982 HHH mEEosoHEo mH. magmas onHm m m 8288882 m. .582 m 88::on ow magmas 3.89 m H. 3.82 s .HHHHmmEmo om 8382882 8 magmas H82 8 m .3sz 2 8288882 HHH 83:02 8 38885 .mccnm 2:5 mm 3 82.2.80 H.H .HHHHHomSo cm 38820 mm 388830 233 fiscoacav Eco EchmeO Eco EmwscwHO Eco EmHHHcmHO Eco Emwscwao Nwewfi Ihmnw >H Ihmnm HHH uhmnm HH Ihmnm H mid; p08 .HcfiO coccpnsooo .Ho xcmm H mpccwsoo nomEOHm 133 .«o cEHHHo> .Ho “ccocca .3 pcxsch cme :omc H: 30.3 Bongcn mo mEmHscmno poo.“ 3305.3 .Hsom mm cEcB 102 Predatory animals On the occasion of each visit to the lakes a close watch was made upon approach to note the presence and activity of any predatory animals. A number of predators were observed on these visits. A pair of loons spent most of the season on Doyle Lake. An otter was observed once at Marl Lake and once at Little Lake. American and hooded .mergansers were observed on Slide and Marl lakes. Great blue herons were observed at Bass, Ryan and Marl lakes, and a nest of green herons was found in a tree overhanging Norway Lake. Each lake was visited oncexevery 2 weeks throughout the 1960 season. If more visits had been made,especially in the daily crepuscular periods, I am sure many more predatory animals would have been observed. About 40 northern pike were gill-netted during the season in Ryan Lake. Several more were found dead following the rotenone treatment. The pike averaged slightly over 17 inches in length. One fingerling trout 10. 5 cm in length was found in a pike stomach from Ryan Lake in July. It is probable that these pike entered Ryan Lake from the Denton Creek outlet sometime before mid-April and thus were present in the lake the entire season. A large (length 51 cm) northern pike was killed in \the October, 1960 rotenone treatment of South Twin Lake. I doubt if this pike had been in the lake all season.6 Water snakes (Natrix sipedon) were seen at Marl, Doyle, Ryan, and Bass lakes. I believe they were present around all of the 6 It was rumored that a local man introduced the pike just before the rotenone treatment to see if it would be recovered in the treatment. 103 lakes except Little Headquarters. In May, 1959 a water snake caught a legal trout on Marl Lake shortly after the fish were planted. , Snapping turtles were observed in every lake except Little . Headquarters. Turtles (several species) caused the destruction of about 320 trout in the gill nets. It was noted in night observations with submerged electric lights that adult snapping turtles frequently swam. in the vicinity of concentrations of trout. On two of these occasions in Marl and Slide lakes live trout were captured with a large wound in the dorsal area; these wounds were about one and one- fourth inches long and one-half inch deep. It is doubtful that these fish could have lived for more than a few hours. It is possible that the wounds were bites inflicted by the snapping turtles. DISCUSSION AND FURTHER EXPERIMENTS The stocking of trout in waters where they cannot spawn, or maintain a self-sustaining population through recruitment, is a problem of efficiency in making trout of satisfactory size and appearance avail- able to the angler in the greatest quantity. A high rate of depletion in numbers can be expected from the time of planting throughout the existence of the population. Through growth in weight of the individual fish an expansion of the original biomass can be expected, utilizing the food produced in the lake environment. Production is offset by loss from natural mortality. The question of how best to manage for maximum angler harvest entails a determination of the size and num- bers of trout to plant, and selection of a lake environment to assure a high rate of growth with a low rate of natural mortality. In this discussion, attention will be given first to the environ- mental factors controlling growth of trout, and next, to environmental factors influencing natural mortality. The interaction of growth and mortality will then be discussed with regard to efficiency of the trout pepulation in providing a maximum stock of trout for the angler. Lastly, the relationship of temperature as it affects rainbow trout in the lake environment will be reViewed from the literature and from the experiences of this study. 104 105 Environmental factors influencing growth The growth in (weight of the individual trout varied significantly between the p0pu1ations in the ten lakes. The magnitude of this dif- ference in growth was large as at the extremes of the range, trout in Little Lake (269 grams) averaged nearly 2. 5 times as large as those in Ryan Lake (110 grams) at the end of the 1960 season. The dominant environmental factor that influenced absolute growth was the biomass of the total fish population in each lake. The Spearman Rank Correla- tion Coefficient between absolute growth and total fish biomass (trout and other species combined) was rs = . 806‘”. This coefficient is positive as the p0pu1ation exhibiting the greatest absolute growth was ranked number one, and the p0pu1ation with the lowest biomass was given first rank as the dependent variable in the non-parametric Spearman test. A linear regression computation was not possible as the: total biomass was known only on an ordinal scale. Considering the relatively low power of the Spearman Rank test, however, it is apparent that the relationship between absolute growth and p0pu1ation density would also have been highly significant with the parametric linear regression analysis. The significant relationship between large absolute growth and low total fish biomass in these lakes is most likely due to the fact that several of the populations were below the hypothetical carrying (capacity of the lake and thus growth was influenced by the food supply 106 available to the individual fish. All of the lakes were treated with O. 5 ppm of rotenone in the fall of 1959. Four of the five lakes (Table 23) in which greatest absolute growth occurred cOntained trout-only fish populations. The fifth (Doyle Lake) contained only a few redbelly dace. Four of the five lakes exhibiting lesser growth of trout contained sizeable p0pu1ations of non-trout species. These four lakes probably approached carrying capacity much more closely than did the lakes with trout-only populations. Confronted with the close correlation of absolute growth to total fish biomass it is difficult, if not impossible, to assess other environmental factors influencing trout growth in more than a specula- tive sense. The decreased rate of growth in July and August from high temperature does not appear to lessen absolute growth for the season as a whole because it is compensated by very rapid growth in Septem- ber and October (Fig. 9). It is possible that the relative size of the littoral zone in each lake was an underlying factor of importance in determining the absolute growth through control of the relative quantity of food produced. The food habits study indicates that benthic organisms provided the bulk of the trout food in nearly all of the lakes. Ball (1948) found that the littoral zone in a southern Michigan lake produced the bulk of the food of the bluegill. In this lake the littoral zone was determined as the area from shore to a depth of 107 mp. war.“ we. emw. o: schm scam cTnoQ schm comm N mm. mm .3 mm. emm . o3 eHmoo 222 H32 5.5. .m 5.3. .m on we; 3k: mm. Nmm. mg 5.5. .2 2:3 E5. .2 .8382 $382 E> EA 3 .2 mm. m3. m2 :32 .3382 schm mmmm mmcm HH> mmé. 5.2 we. mam. :m .53902 539 .m .mpcom 332 53H. . 2 Cr rm .H mm .3 ow. coo; omm 53H. .m 2.53 .AmBnoZ choQ cofim > SA No.3 mm. 3o; mmm .335 .235 2:6 £5. .2 H.842 E :4 3.3 mm. mmoé 5m 2:8 55. .z 2:5 3:5 eHaoo HHH oo.m mmdm ma . mmoé mom mwcm mmcm mmcm .933“ .9153 2 rod mm.mm S . so; mew c354 ccfim 53H. .m c334 c334 H Acpoc . ... hoccwoflmc .Hca 25:03 52.3.88 M 68¢th .833 Ewwck VHS... m 95.ch m . so 3960.5 1..“ch choh. cofiwocoo coca: 35h owmfi .mmcoo3m «no.3. mo macacgmhma c5 09. mgopoooc comma nocc mo 58m .mn cScH. 108 3 meters--the lower limit of submerged plant growth. Johnson and Hasler (1954) consider the "life zone" that volume of water containing more than 3. 0 ppm of dissolved oxygen as the food producing zone for rainbow trout of Wisconsin dystrophic lakes. The relative size of the littoral zone to a depth of 3 meters, and the oxygenated volume,containing over 5. 0 ppm (also more than 0. 0 ppm) dissolved oxygen,were portrayed in Figure 21 for each of the ten lakes in this study. I found that the correlation coefficient (r) between absolute growth of trout and large littoral zone as defined by lake bottom area to a depth of 3 meters was r = . 80 If". This correlation was greater than absolute growth to the lake bottom area of the (zone containing over '3. 0 ppm of dissolved oxygen (r = . 661*) and much greater than to the bottom area of the zone containing more than 0. 0 ppm of dissolved oxygen (r = . 282‘). These relationships, however, are subject to question in light of the correlation between growth and the total biomass of fish as discussed previously. No relationships were apparent by inspection‘between alkalinity or hydrogen ion content of the water and absolute growth of the trout. It is possible that the relative size of the littoral zone and the total biomass of the population are both dominant environmental factors in regulating trout growth. Both factors Operate to regulate the food supply available to the trout. The size of the littoral zone is of importance in determining the total supply of food. The density of the population determines the rate of cropping of this food. The size 109 of the littoral zone was fixed in the individual lakes, but the density of the population could fluctuate over a wide range. Thus the food supply produced varied between the lakes, but population density was the immediate factor that determined how much food was available to the individual trout. Turning to discussion of trout growth in the individual lakes several observations can be made which shed additional light on the relationship of trout growth to the available food supply. In Bass Lake the growth of the rainbow trout (Table 8) was rapid until about the time of the June bluegill hatch after which the rate of growth in weight declined rapidly until it was negative in value. Bass Lake has a small littoral zone. Only 28 percent of the bottom is included in the .0 to 3 meter range of depth. It seems apparent that the trout population had an ample food supply until the bluegill hatch occurred. The combined-species fish population probably expanded rapidly thereafter, depleting the food supply to the point that the trout could not meet maintenance requirements. Ryan and South Twin lakes show a slow growth ratevof the trout all season. It is believed that each of these lakes had a relatively high population of non-trout species all season and that the food supply was insufficient to allow the trout to make rapid growth. It is also possible that the metabolic scope for activity of the trout was lower than that of the competing species making the trout a relatively poor competitor for the available food when other fish species were present. 631 W E 31 110 The reasoning expressed above seems to be completely con- tradicted by the trout population in NOrth Twin Lake. This lake has a small littoral zone, and Contained a relatively large biomass of trout and non-trout species. Yet trout growth was fairly rapid (Table 23). The explanation may lie in the fact that North Twin Lake is atypical compared to the other lakes. This lake received a heavy organic enrichment from slaughterhouse wastes. The population of Cladocera was high throughout the season, and undoubtedly the production of invertebrate bottom organisms was very high in the small area available to them. Apparently the food supply was sufficiently high to allow rapid growth of the entire population. Norway Lake, on the other hand, had a relatively low growth rate although no fish other than trout were present. NOrway Lake has a precipitous basin lepe starting almost at the shoreline. The water is soft and very turbid throughout the season. Consequently, the available food supply of benthic organisms is believed to have been very low. The food habit analysfis (Tables 21 and 22) corroborate this view as littoral benthic organisms made up only a small portion of the trout food. It would seem that the mean standing crop of 16. 9 pounds per acre was nearly equal to the carrying capacity of this relatively unproductive lake. In the remaining lakes trout growth was fairly rapid and did not differ markedly between lakes. All (of these lakes contained trout- only populations. There was a slight indication that growth was reduced as biomass of trout increased. 111 1961 experiments on competition affecting trout growth The finding, from the 1960 studies, that relative size of the standing crOp of fish was the dominant environmental factor affecting absolute growth of trout prompted a decision to use the 1961 year of field investigation for further experimentation in this area. Five lakes from the 1960 studies, namely; Doyle, Little Headquarters, Slide, Little, and Ryan, were selected for the 1961 investigations. Each of these lakes had been treated with rotenone in October, 1960 to eliminate the fish p0pu1ation. They were stocked on April 20, 1961, at various rates to establish markedly different biomasses of fish in each lake (Table 24). The objective and results of each lake . experiment are summarized in the following paragraphs. Doyle Lake. --This lake was selected as the control, and planted at nearly the same rate with rainbow trout in both 1960 (20 pounds per acre) and 1961 (23 pounds per acre). The slight differ- ' ence in planting rate resulted from the fingerling trout being of larger size in 1961.,7 The growth rate of trout was nearly identical in both years (Fig. 23). 7The fingerlings planted in 1961 had a mean weight of 12 grams as compared to a mean weight of 1. 1 grams for the 1960 plant. These fish were the smallest fingerlings available from the hatcheries in 1961 and thus were planted in Little, Marl, and Little Headquarters lakes, as well as Doyle, in these experiments. 112 .Hca menace wcwxoowm .3 camp c5 op :oflmficp 5 5%ch 5 53on «no.5. 309.me mo QOmEmQEoO £2chan hmchtmoumcsom Hob sofiflcafioo ow new. Acpoc HMU_ mm.“— m:<_ 2:. _ 2:1_><2_.mn_< I - .8. 2.333% 5m. 3: 033 + 9.3 8.5 9. a... 9.2.2.33: 2:... 9. a... 2.60 .mm .mE OO. 00m 00— CON oon SWVUQ NI .LH9I3M 113 Little Headquarters. --The rate of planting of both legal and fingerling trout was approximately doubled in 1961 (36 pounds per acre) over the 1960 rate (17 pounds per acre). The increased biomass in 1961 caused a significant reduction in final size. The final mean weight in 1961 was 198 grams as compared to 291 grams for the NC8 group in 1960. The condition factor (K) showed a corresponding decrease frOm 1. 071 (1960) to .971 (1961). Slide Lake. --The rate of planting of trout was approximately the same in 1961 (23 pounds per acre) as in 1960 (21 pounds per acre). These planting rates correspond with those in Doyle Lake. In Slide Lake, in 1961, approximately 50 adult bluegills were released just after the trout were planted. ‘ These bluegills comprised less than 5 percent of the trout biomass. The objective was to determine the effect of their young-of—the-year progeny on trout growth, not of the adults alone. A good hatch of young bluegills occurred in June and they were observed in abundance thereafter until the final trout col“ lection in October. The final mean weight of the legal trout in 1961 was 164 grams, as compared to 260 grams for the NC group in 1960. The 1961 K factor was . 895 compared to 1.042 for the NC group in 1960. Little Lake. --This lake was planted at approximately one- half of the rate in Doyle Lake with legal trout in both 1960 (9 pounds 8Comparison of absolute growth of. the 1961 legal trout is made with the 1960 NC group in Doyle, Little Headquarters, and Slide lakes, because these groups were both planted in April and are more directly comparable. In Little Lake the comparison of trout growth in 1961 must be with the 1960 A and LP groups as no NC fish were available. rn 114 per acre) and 1961 (10 pounds per acre). In addition approximately 50 adult. bluegills were introduced with a hatch of youngeof-the-year progeny the same as in Slide Lake. The final mean weight of the legal (trout. in 1961 was 169 grams,» as compared with 269 grams for the A and LP groups in 1960. ' TheK factor of .889 in 1961 was much lower than the K factor of 1. 087 in 1960. Mnkaig. “Only 200 legal trout were planted in 1961 as compared with 1,480 legal and 1, 440 fingerling trout in 1960. Further, the barrier. screen remained intact throughout the season and the biomass of non-trout specieswas much lower than in 1960. With the reduced biomass the trout grew rapidly in 1961. Twelve trout caught With gill nets on August 17, 1961,. averaged 30. 1 cm .in length, and 2952’grams in weight. Anglers reported catching trout from 13 to 15 . inches in length in late August. ' On October 26 only-2 trout were taken. in the gill nets (28. 5 cm -in mean length, 216 grams mean weight). All of these trout were larger than the final size of the‘trout in 1960 (average weight NC group, 112 grams), indicating that the poor trout growth in Ryan Lake in 19 60 was due to the large biomass 0f fish present, not to other physical or chemical characteristiCs of the lake. The results of these experiments (except Ryan Lake) are summarized in Table 25. In Figure 23 the results are portrayed graphically. In 1960 at planting rates of 9 to 21 pounds per acre the trout in all four lakes grew at similar rates. In Doyle Lake in 1961 115 Table 24. Summary of trout stocking statistics for experiments on effect of trout population density and young-of-year bluegill competition1 on trout growth Lake and . Number Pounds Mean Mean , Size . experiment Year class per per length weight ' ‘ ‘num'b‘e'r acre acre (cm) (grams) 1. Medium tr'ou't (1960) vs medium trout (1961) (control) Doyle 1960 Legal 101 20. 0 21 90 1960 Fing. 100 0. 2 5 l 1961 Legal 100 19.8 20 90 1961 Fing. 100 2. 6 10 12 2.9 Medium trout (1960) vs heavy trout (1961) Little 1960 Legal 88 17. 2 21 90 Headquarters 1960 Fing. 8O 0. 2 5 l 1961 Legal 80 31. 7 20 90 1961 Fing. 161 4.3 10 12 3. Medium trout (1960) vs medium trout + bluegills (1961) Slide 1960 Legal 106 20. 8 21 90 1960 Fing. 102 - 0.2 5 l 1961 Legal 102 20. 2 20 90 1961 Fing. 102 2. 7 10 12 4. Light trout (1960) vs light trout + bluegills (1961) Little 1960 Legal 42 8. 5 21 91 1960 Fing. 84 O. 2 5 1 1961 Legal 42 8. 3 20 90 1961 Fing. 84 2. 2 10 12 1Approximately 50 adult bluegill spawners released in Slide and in Little lakes in 1961. 116 .Sm 8. 2 5.34 82.3... 3:on Hanan 8:6 HH... em .32 oooooHnHm .mm .8880 2:858 mason. HemH one 82 fiomN .w «mnmn< no pc«ocSoo anonw 33 Mom .33. no Uc«oc:oo nnonm cmmHH 3H .- 2... mm... 2: 5 NH... EH 5 om om Hemoq HeoH -- --- 2.: new mm 9...: 2: ea Ho Hm mHmwon 82 235 new: 253an + «sob Eu: 9. 82.: no.5. EH: .H. SH .- 2.. mom. 2: em 2... HM: 2.. H... on Hmwon H2: 2 -- 35H 8” mm mom. 3H 5 om Hm Howoq 82 oEHm :8: 25133.. + «so: 83.88 m> 8...: C. «so: 83.82 .m ooH .. 3.. :2. in R 2a. 3H 3 oo om Howoq $2 285385 E. -- HSH How om when an em om Hm Homon 8H: £an :3: «ooh .caon h> 82.: «so... 8382 . .N moo .+ .1. mooH new on 80H mum on cm on Hmmon HeoH .. .,-. eoo .H 2.... on So .H mm: 5. oo Hm Homoq 82 £28. :33 «no.5 5338 m> 83: «no.3 8:882 .H Amendpmv $5.33 $23 Amnnwhwv Annoy Acachmv Annoy {Hogans M Ems? M «same? 533 M «an....» £984 Ewe...» 5284 95% «no.2. «5823.... .HSH: 888:5 «Hour... Heofifiomonz HmnHoH o5 8.3 In! 530nm «no.5 no noflficafioo «fimcng acchumotwnn02 .«0 0nd .nfimnco nofiamnaon «no.5 . .«o c«octc c5 no 3:25.398 5 «no.5 50 .853 nofifinnoo ES .232» .H««wncH no 28339.80 .3 canon. 117 (planting rates of 23 pounds per acre) the trout grew at a similar rate to ~ 1960, but in Little Headquarters Lake with the‘planting rate doubled . growth decreased by nearly 50 percent (from 201 grams in 1960 to 108 grams in 1961). ‘Apparently this heavier rate of stocking caused the biomass of trout present to pass some critical point of the food supply whereafter growth dropped sharply. It will benoted from :Figure 23, that the absolute growth rate remained relatively constant throughout the year in Little Headquarters Lake with a trout-only p0pu1ation. In Slide Lake and Little Lake (1961) the young-of-~year bluegill population reduCed trout growth approximately 50 percent from. 1960 similar to the effect of the double rate of trout planting in Little Headquarters Lake. The growth curves in .Figure 23 showthat the trout in Little and Slide lakes made practically no growth in weight after mid-August. ' This is the same phenomenon observed in Bass Lake in 1960 (Fig. 9) when troutigrowth ceased by mid-August following a bluegill hatch. The light rate of trout planting (10 pounds per acre) in Little Lake had no practical effect in sustaining trout growth, over the medium (23 pounds per acre) rate of trout stocking in Slide Lake, after the bluegill hatch occurred. It is apparent that the rainbow trout can grow rapidly in any of these lakes at low population levels (less than 20 pounds per acre). 7 However, either increasing the biomass of trout materially, or adding competing species of fish. to the population, will suppress the rate of growth. The first-year progeny of a competing species such as the 118 bluegill demonstrates in these studies how severe inter-specific competition can be in limiting growth of the trout, as in nearly every instance trout growth declined to practically zero within a few weeks after a bluegill hatch. {There is certainly a reduction in the food sup- ply available for the individual trout with any material increase in total fish biomass. lt is possible that some sort of "crowding factor" operates to limit trout growth beyond simple food supply in the mixed species p0pu1ation. There is evidence that temperature controls metabolism of these various species in water above 65 F and renders the trout the poorer competitor (cf._ discussion on temperature). The lakes in the 1961 experiment had been poisoned with rotenone in both the spring and fall of 1959 and in the fall of. 1960 to eliminate'tthe existing fish populations. In Figure 24 the mean growth in weight of each successive trout population in Doyle Lake is portrayed. Although the actual mean standing crop of trout present was not ascer— tained in 1959 and.1961,it is believed that the standing crop was materially larger in each of the successive annual trout p0pu1ations. There is no evidence that the repeated rotenone treatments adversely affected trout growth, rather, there is some indication that the growth rate was more rapid in 1960 and 1961 than in 1959. Mortality 'Fishing mortality has been discussed'ear‘lier in this paper so only natural mortality will be discussed here. The-irate of natural mortality was closely estimated in each lake. but little is known of the 119 mcwccmwm coma 2E. .3200 595.com $39.4 _ 32. 2.2. .32 _ .54 .82 5 $22: 28 .82 E 8:2: .22 5 Egg 2: was Bob 20 no.8 .82 .82 .22 8:3 2.80 5 Bot no 539% 838%. no somflmafioo .em .mE m4:._. 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Brook trout Central mudminnow Northern pike Northern redbelly dace Golden shiner Common shiner Creek chub White sucker Black bullhead Yellow bullhead Brown bullhead Brook stickleback Green sunfish Pumpkinseed Largemouth bass Black crappie Johnny darter Yellow perch Scientific name Salmo gai—rdneri Richardson Salmo trutta Linnaeus Salvelinus fontinalis (Mitchill) Umbra limi (Kirtland) Esox lucius Linnaeus Chrosomus eos Cope Notemigonus crysoleucas (Mitchill) Notropis cornutus (Mitchill) Semotilus atromaculatus (Mitchill) Catostomus commersoni (Lacepede) Ictalurus melas (Rafinesque) Ictalurus natalis (Le Sueur) Ictalurus nebulosus (Le Sueur) Euc alia inconstans (Kirtland) Lepomis cyanellus (Rafinesque) Lepomis gibbosus (Linnaeus) MicrOpterus salmoides (Lacepede) . Pomoxis nigromaculatus (Le Sueur) Etheostoma nigrum Rafinesque Perca flavescens (Mitchill) 1of. American Fisheries Society, 1960. A list of common and scientific names of fishes from the United States and Canada. 2nd Ed. Spec. Publ. No. 2, Am. Fisheries Soc., 102 p. 166‘ . . It . : . ’ ‘5‘ t, I a 15"" 'H 1 {l 5‘15"; L'u‘l'" ’l g‘ 1"“